Makes sense to me. Having the phone handle it means it can be done via an app with no internet connection, saving a whole lot of money in maintenance-related troubles. Sure, it also means that some idiot could risk jailtime to save a few bucks on laundry, but who'd be dumb enough to do that?
That's probably the biggest problem - how do you do coin laundry when you don't have an internet connection? In the past, you did it with real coins, and those were a pain to deal with (given it costs like $5 now, that's 20 quarters).
It's not easy to design a system where you can operate offline machines in a way without having to trust something, or having to deal with the aftermath if something goes wrong. You could demand the offline machine get a token that contains the time (encrypted, etc), which is great because it's a way for the machines to keep time and everything.
But what if the token gets corrupted on the way to the machine? You've securely removed the money from the user's account, and the token to a do a load of laundry is gone. Now the user is screwed over. Not a big deal if you're the only guy on campus, but it's going to happen a lot, and schools will get complaints about it and demands to fix it, and eventually it's going to hit someone important.
About the only way is to have the machine use the phone as a router and connect to the company that way, but that raises all sorts of privacy issues and network usage issues. It also raises support issues because if they don't have a phone that works.
Now, you can rely on the fact the machines will be serviced on a regular basis - there will be someone who will go around to make sure the machines are working and to stock up the vending machines for detergent and other supplies. What can be done is the machines all log the IDs used and the accounts are billed afterwards. This is usually combined with a stored value card that caches how much is on the card. Sure the student can rewrite it, but the audit log would show how many loads were actually done and the proper amount can be deducted even if the cached value on the card is incorrect. But it still means someone can get a bunch of free laundry done because they're leaving at the end of the semester so who cares.
The final way is to install an offline credit card machine - you do laundry you tap your card. Someone periodically downloads the transactions and posts them to the credit card account. The problem with this is the erratic posting - you do your laundry and it only shows up on the credit card bill a week later.
But yes, that's the fundamental problem - the machines may be placed in a location where there is no access to connectivity - cellular, WiFi or network. Coming up with a reliable payment system for this is extremely difficult - it's possible, like I said, credit cards can work offline (the old kerchunk machines were completely offline) but you do run into issues in that mode of operation especially if records aren't kept properly, receipts, etc.