I can see one very good reason. The store is like Steam. Say they suffer a massive security breach like PSN did. I think that's grounds to sue.
There's also the speculation of other parts of their EULA, regarding you losing your games if you don't log in for a set amount of time. (Two years I think it is.)
Not to mention if they sell you a game knowing it's defective or broken in some fashion. (Like the recent From Dust debacle with Ubisoft.)
The fact is it should NOT be legal to have this in the EULA IMO. I would guarantee it wouldn't stand up in court. The only problem with that is you'd need a lot of money to do it.
I also love the way the EFF never say a bloody word about stuff like this. Finding the EFF increasingly pointless.