Don't see the big deal. Bing is nicely integrated into Windows Phone, and with Google being a real **** towards Microsoft, no chance of any integrated, comparable search being available on Windows Phone except via Bing.
I don't get the hate towards Bing, it gets the job done well as Google. Honestly, for me, the search results on both seem to be exactly the same, so I just use Bing because:
1) The days, I do at least 70% of searches on my phone, and Bing is just a button away.
2) Bing rewards are nice. Not anything stellar, but a nice bonus every once-in-a-while.
Anyways, aside from complaints about Bing vs. Google, I also don't get the whole Bing button complaint. I rarely ever hit it, and if I do, just press back and quick-resume right where I left off (Unless the app doesn't support a simple feature that's been out since Mango, in which case, I have a few choice words for the developer...). I guess Microsoft could add a toggle, but in my opinion, that's a slippery slope.
User customization is nice, but you've got to draw the line somewhere. If you start adding toggles and exceptions for every little niche and single consumer, you eventually end up with a cluttered, toggled-up mess that lacks appeal and is less user friendly. Thus is/was the problem for Android, trying to hard to accommodate everything. It's been easing up in recent devices, but nonetheless, it does look/feel cluttered at times.
That, in my opinion, is the appeal of Windows Phone. I feel that Microsoft got the balance between unity and customization just right with their Metro interface. It can be customized enough that each and everyone's device has its own feel and flare to it, yet remains familiar enough that anyone can pick it up and instantly know what they're doing. iOS accomplishes this too, but it has even less customization, so no real difference between devices other than the wallpaper and where the apps are in the grid. I guess that works for some, though.
Sorry for being a bit all over the place, I write as I go along, and my mind tends to wander. I just hope my post got some point across and contributed to this thread in some way.