Do consumers actually differentiate on these extras? I don't think I've ever heard anyone say "Yeah I picked up a Lenovo laptop because the antivirus they package is better than Dell's" or "I got a Samsung phone because their skins are better than HTC's" I'd love to see the market research that backs that idea up...

I thought the real reason manufacturers do this is because they're in a very low margin industry. For computers they get some deal with software companies to pre-install their product, and similar for cell phones with service providers.