the custom homescreens aren't necessary...but they also aren't "mandatory"...so why not?
I like having the choice. I can choose from Titanium, sense 2.1/2.5, mobile shell, PointUI, Androkidd...it's nice to use whatever you like as long as the user always has the option to go back to titanium which is worthy in it's own right.
To be honest, the palm pre is actually...pretty stylish? I know...shocker from Palm...but I wouldn't mind borrowing some of that design and maybe the apps from android...android is still young, but there are a good number of apps with some great polish to it. For some reason the larger developers don't seem to sign onto apps for WinMo like they do for the iphone/android/ and even blackberry/ which hurts. XDA keeps us going though!