Yeah,its because people can buy them off the internet,print them off,then scan through without their ticket being checked. Same could be done with season tickets too worryingly.
Apparently in the UK,you cannot buy concession tickets online and just print them off. You have to either go buy them straight from the shop,or buy online and pick them (on matchday). Either way there is an ID check. But 2 problems with this method i guess are....
a) you could just get a child/student to go pick up the ticket,then give it to you to use.
b) It would put people off because of the inconvenience factor.
The only other solution is to check EVERYONEs tickets as they enter the gate. This also has obvious problems of...
a) would cause a big logjam as people are traditionally good at arriving at the very last minute,and would take forever for 8-10k tickets to be checked.
b) the cost of the extra security that would have to be on to check all these tickets may outweigh the benefit of the cost saved from those who partake in this ripping the club off practice.