10 years is an eternity in tech years. Even six years is pretty ancient. If you never upgraded anything (OS, software, etc) maybe you'd get away with it but eventually you'd run into things not being compatible due to age. 10 years isn't realistic, in my opinion, especially when you're taxing it with a program like Photoshop. My Macs have lasted about 4 years with daily PS use and even then I saw a huge jump in speed when I upgraded.
As far as MacBook vs iMac, I could never give up my MBP because the portability is more important to me than a large screen. But I also have an Apple display that connects to my husbands Mac mini which I can connect to when I need more space. It's the best of both worlds but I definitely move the MBP around more than I plug into the screen.
Just to give you an idea, Mavericks is only compatible back to 2008 which 6 years. Older than that and you'd be out of luck:
http://www.techradar.com/us/news/com...ake-it-1064310