Valve's cut was never smaller compared to competitors. There's a reason why they insisted on all the terms of their deals (and sales numbers) being secret; they are still really brutal about not being able to share contract terms or revenue numbers.

Hell, I shipped a fucking game on Steam and I don't know what the % we gave them was (though I could probably figure it out by doing enough math on the sales numbers...)

One thing I do know (second-hand information, but from an expert) is that they even demand a huge cut from F2P games, despite the fact that F2P games have their own download, patching and payment infrastructure. They literally charge as much as they can possibly get away with, even when they offer near-zero service.

The quality of the services Valve offers for your money is also fairly low. The Steam API breaks constantly (usually because they are haphazard about changes and have near-zero automated or manual testing), is poorly documented, and is infrequently maintained. Valve can and will ship a Steamworks update that breaks a core part of your game, and leave it broken for weeks no matter how often you complain - unless you happen to have the phone number of someone at the company, or send them numerous emails. The APIs that do work are slow and limited. It's better than nothing, certainly, but not so magnificent that it's worth 30%, especially if you compare it with something like GAE or EC2.