"Applications close when I want them to, and stay running in the background when I want them to."
With windows mobile you have no control on which applications can stay open and which can't. If you do it's because your phone has some third party software in it that hacks the X button behavior.
"I can access a list of running applications at any time."
Where "any time" means having to go to the start menu and keep scrolling two-three pages until you reach the bottom where the task manager is and then launch it? On WM 6.5, where the scrolling halts at each page, it's going to be uber-awesome. All of this if your phone hasn't yet another other ugly task management hack done by the phone manufacturer.
"I've never actually had it run out of RAM, so I don't know about that problem you describe."
You don't? Then I wonder why the latest phones models have 256 or more mb of ram. I'm sure the phone manufacturers love investing in useless features.
"I also haven't touched the stylus in months. Wait, that's not right. I used it to scratch a really bad and hard to reach itch in my ear a while back.
"
You don't? Then how do you tap all those small notification icons, for example to set the phone volume, or check the battery status, how do you select text properly or how do you use all those tiny scrollbars or the incredibly small on-screen keyboard?
This is the WM default keyboard, can you really tell me you can type on this, with your fingers, on a 3'' or smaller phone screen? If you can then you must have the smallest fingers in the world.

Windows Mobile has an awful UI, if you can manage to do something without pulling out the stylus it's just because your phone manufacturer did tons of ugly hacks and applications replacements to make the UI more usable or you have a ginormous PDA phone with a QVGA screen.
"Oh, look, the DSL is being flakey. Let me set up my phone as a wireless hotspot, aaaand off we go."
Just another third party app included by the phone manufacturer.
"Oh, it would be nice to have a bigger screen and a faster processor, (Although the latest builds of 6.5 are pretty snappy) but I want it to be on my terms, not subject to the whims of some designer somewhere. I really like that it's almost infinitely customizable."
You can try all the faster processors you want: with WM having a nearly inexistent UI acceleration the phone is always going to be laggy.
"I also like a hardware keyboard."
Which keyboard? The Touch Pro keyboard that has no left/right hardware buttons, OK and start menu buttons or the Xperia X1 keyboard that has no directional arrows (unbelievable but true).
"I like being able to access websites with flash, but it would be nice to have an adblock feature."
Flash use is primarily for ads. With flash lite you can view only a subset of flash animations: only those that are designed for flash player 8. Is it really worth having all your page loads slowed by all the websites' ads just to see youtube and some other lame flash animations?