Well, I am a proud HTC Hero owner, but I just came from the HTC Diamond and a lot of my friends have the iPhone and some have Blackberry's.
I think that it is a 'to each his own' type of deal when your talking electronics in general. Windows Mobile and Blackberry OS's are great for business orientated consumers that use a lot of push mail. Windows Mobile is very customizable, and you actually said it for them. Windows Mobile users can make their OS look however they want! They can make it look more like an iPhone or more like TouchFlo3D and even I guess the Hero's Sense UI. That is customizing I could live with (and did). The OS on my Diamond was occasionally laggy and slow which is why I switched to the Hero. I still experience some lag and slowness with the Hero as well.
I iPhone is semi-customizable, but not to the degree that Android seems to be. Widgets are sweet and multi-taking makes the Android OS a handsdown winner (for me). The iPhone is a gadget device, while extremely powerful in some aspects, lacks open-source and a good carrier. (I am not a fan of AT&T in my area, bad reception for most ppl and seems like iPhone users drop too many calls).
Blackberry is good for ppl that don't want a toy phone but for business. It lacks a lot of fun tools but does a great job at what it does.
I guess the point to my writing this is each device, each OS, each carrier has something unique to bring to the table and it truly depends on what YOU want and desire. Not to mention you are on a PPC forum and these people do like WM for a reason, if you want backing, head on over to a strictly Android forum and I'm sure everyone will agree with you there
While you say that WM devices need tweaked... the only reason I tweaked my diamond (or even found out about all this ROM stuff, even this forum) was because I had terrible battery life.... the Hero is suffering from a similar fate currently for some users. Other than that the OS was sufficient for a year or so ago and I was happy with the device.
... Nevermore....
The End