According to zdnet, a somewhat reputable source, Jobs "laid out plans to enable the popular iOS, iPod and MacBook products to continue for years."
http/www.zdnet.com/blog/btl/jobs-left-future-plans-for-next-generation-apple-products/60178
So unless Apple makes a claim in the future advertising of the iPhone 5 that this is the last device Steve Jobs worked on, then I doubt it will make a difference to their sales.
Personally, I think it would be really bad for the company to use that concept because they run the risk of every product after that being seen as inferior. While Steve Jobs had exciting ideas (some new, some borrowed, some improved upon), he wasn't the sum total of development for Apple. He put together an exceptional team and infused them with his vision so that it could carry forward.
For the record, my phone is the Nexus S, my laptop from Samsung and my desktop from various manufacturers, with some stuff from Microsoft as well. My wife has the iPhone, iPad2 and MacBook Pro. A mixed marriage, but we make it work.