Maybe the reason the reason we don't do it is because nobody lets us?
I'd *love* to have Blend for my Blackberry Z10. I love my Blackberry Z10, it is by far and away the smartest messaging and communications device (that's what my phone is for after all) out there. It does facebook and twitter too if you want to waste your entire life doing that.
It does most of the other rubbish everyone wants too - some not so I admit, but I couldn't care less because I value being able to reliably communicate and do my job over some ability to potentially check the latest bill I got from $randomvendor via an otherwise featureless app. Especially when said vendor has a web site that works just fine on my phones browser.
The same integrated any device approach Apple are developing is the only thing I actually like about what apple are doing - I still wouldn't buy the products they churn out though. I'm actually amazed Microsoft haven't long since done this - they could have integrated all of this in minutes across it's devices and platforms, but as usual they're too busy napping.