There's a couple benefits to buying a boxed set of an online game, free or otherwise.
One is, you don't have to wait for the inital client download. For some people, that alone may be worth the purchase of the disc.
There are also usually box-oriented store incentives, like free AP, promotion codes for exclusive items, etc.
There's also the collector's incentive, just owning a hardcopy may have value long after the franchise has moved on.
It wouldn't be very reasonable to expect people who already play Imagine to get it, of course, but for people who say, don't go around the internet a ton, but <3 SMT, and just happen to see it in say, GameStop or something, it'd be pretty appealing, don't you think?
