History for Yohan

I'm not here to pick a fight. But you asked the question.
 

MLS has soccer specific stadiums going up everywhere. Recently built Red Bull Arena in NY cost 250 mil. Sporting Park at 200 mil. Not only do SSS create better game day experience for the fans, but the fact that MLS teams can build SSS at such a cost demonstrates financial power. Heck, even some lower division teams have SSS (though on smaller scale) like San Antonio and Charleston, with Carolina and Pittsburgh planning their own SSS. 

With good infrastructure, MLS teams average 15-19k in attendance. Even some lower division teams get decent attendance with San Antonio at 9k and Orlando City at 8k. 

This means MLS can afford to spend a bit more on player wages. While this season's salary cap is 2.95 mil, in reality, each team spends about 4 mil, excluding designated player (marquee player) salary. (This is from MLS commissioner btw) MLS has this thing called allocation money which can be used to 'buy down' a salary, or used to pay transfer fees. 

I'll agree that MLS domestic talent pool is comparable to A League domestic talent pool, though MLS and US is starting to spend a lot of money on youth academies and such. The difference is access to international talent pool. On top of the scale, you have LA paying 4 mil in transfer fee for Robbie Keane, who makes a yearly wage of about 4 mil. Obafemi Martins also cost couple of mil in transfer fee. A lot of designated players make about mil plus per year. (though there are players considered a DP due to their transfer fee, and don't make a lot of money) And more MLS teams are willing to pay big money for quality players, if the price is right.

Beckham is a bit of attention whore, but his signing opened up MLS to world's, especially European attention. With more understanding of MLS, more players became willing to give MLS a shot, especially combined with high profile signings like Thierry Henry, Rafa Marquez (who sucked so bad, that he had to be ditched btw), Nesta, etc. MLS has gone from a retirement league, to a league that attracts international talent still in their prime years. Average age of designated players is 29. I think if an ex EPL player signed for A League, he'd probably be a marquee player. When Vancouver signed Nigel Reo-Coker, 28, formerly of West Ham and Aston Villa on a non DP contract, he was just another international player. MLS can attract players like Alessandro Nesta, Arne Friedrich, Reo Coker, Mikael Silvestre on non DP wages. I don't think A league can. It also helps MLS that there is a perception that US offers a high quality of life. Oz/NZ also has high quality of life, but generally, people don't know that. (I've been to Oz and I loved my time there)

It's not just European players coming to MLS. With poor European economy, especially in Spain, Central and Latin American players are looking to MLS as intermediate step before going to Europe. Before, they would try to make straight jump to Europe, usually via a 2nd or 3rd tier European leagues. Now, players like Matias Laba, former Argentinian U20 player and only 21 is willing to come to MLS teams like Toronto, when only few years ago he'd be going to Spain. 

MLS player list 
This has the list of all the players in MLS, plus their salaries. I suspect you'll note a lot of familiar names on that list.

So, MLS has access to international talent pool wider than A League. A League also has restrictive foreign player quota, which limits quality of the league. MLS also has international player limit, however, each team gets 8 spots out of 30 player roster, which is tradeable. Also, it is pretty easy to get US green card after like 2 years, which makes int players count as domestic players according to MLS rules. So while US domestic players may suck, the number of int players on a roster tend to balance that out.

Even US domestic players are getting looks. European teams (and Latin American teams) want to tap into lucrative US market, hence why even mid to low table EPL teams like Stoke City and Swansea want to schedule summer friendlies in US, along with powerhouses Man U, Chelsea, Barca, Real Madrid, etc. The trickle down effect of these teams playing friendlies against MLS teams is that MLS players get scouted. The Jan transfer window had 3 MLS players being signed by EPL teams. (Brek Shea and Geoff Cameron to Stoke, Kei Kamara on loan to Norwich, but he has returned to Kansas City recently) MLS players go on so called 'training sessions' with European teams all the time, which are trials in disguise. I think every MLS team had 2 or 3 players go on these 'training sessions' over the winter. One of them, Andy Najar who played for DC United got noticed and signed by Anderlecht. Najar is a 'homegrown player', basically a youth academy product and first one to make the transfer to Europe as a homegrown player. MLS youth academies are relatively recent, and only the fruits of these academies starting to make an impact in MLS. I expect more good players to come out of youth academies, instead of former traditional way of developing players via NCAA (US collegiate system). Simply due to numbers game, a lot of best US players do ply their trade in top Euro leagues, and many of them had their start in MLS.

Last time MLS went fishing in A League for talent, it didn't go so well. I understand that Danny Allsopp was a decent player, along with Fred for Melbourne Victory. Those guys were busts.

So this is why I think A League is about NASL level. A League just cannot compete with MLS's financial power, and without money, you cannot invest in infrastructure and training to develop better players. 

Short version: MLS has helluva more money than A League which it uses to attract better international players than A League which makes MLS better league than A League.