I always upload to facebook Via PC... so I will transfer any images on my phone before doing uploads. Is there any difference if you use the full site through the BB Browser?
I just gave it a try myself by taking a picture of my sleeping cat. I can see what you mean... there's a huge amount of optimisation, and the whiskers look rather pixelated.
Personally I think the app is intentionally like this. It makes sense for those who might not have huge data plans, so the option of keeping every image low quality is an unconditional limitation of the app.