I think that what most people meant is that the 600D doesn't have dedicated buttons for anything of this, except ISO, but then you can't see the ISO setting adjacent to the dedicated button, since the 600D doesn't have any display on top. You either have to look at the back or through the viewfinder. That works as well, but is still features missing, compared to a 60D, for example.
What it does have is arrow buttons that also serve as buttons for WB, AF, picture styles and drive modes. But then, as I wrote before, when you use the arrow keys for immediate selection of AF points, a task which is fulfilled by the joystick on the bigger brothers of the 600D, you have to watch your timing when using these shared buttons, or they do something else than you expect them to do.
The 60D can control two slave flash groups through its internal flash. I don't think the 600D can do this, right? The 60D is also quite a bit quicker in reaction to the trigger button, as well as having a shorter viewfinder blackout. When it comes to continuous shooting, the 60D's buffer depth is quite a bit larger, in spite of being 50% quicker than the 600D.
So there are indeed several differences when it comes to capabilities for these cameras, even if some of them are such that you'll not notice within the scope of a quick comparison at the store's desk, or maybe not even within the first months of use. Several of the differences are mainly noticeable if you do like me, shoot quite a bit of action. But if you don't, then you can often get along with a P&S, or even a decent phone, unless you are iffy about the absolute image quality of your pictures. But if you are, you are probably looking at larger sensor sizes anyway.