Win7 Start can definitely run more than that - there's no hard-coded limit. However, the question is: can it run more than three WELL? - and the answer depends on the applications.
I had a netbook for years - it's even going strong as I refreshed it back to factory and gave it to my neice, so she can do her story writing and homework on it. Works great for her, especially since she's 12, and has smaller hands.