Bing Maps is not very accurate. All road names and addresses are messed up, especially here in Hyderabad... So, if you depend on Maps for traveling, you might prefer Google Maps which is really excellent. (available on Android phones natively)
As for apps, a lot of them are available for WP7 devices as well... You might miss a few if you already have an Android phone or an iPhone. But if you are upgrading to a smartphone from a feature phone for the first time, then you won't notice any problems. WP7 is smooth, good enough for regular use...
Instead of Moto Defy plus, you might want to consider Sony Neo V, if you choose the Android route... Its slightly better...
Cheers!