Its not a matter of "that's ok with me". There are many variables to success. If someone else's "Collaborative Shell Client" takes off and mine doesn't, or takes off in a market I haven't or couldn't service well, and I was on the internet first, I need to review many other variables besides just product design.
and StackOverflow was unabashedly a derivative of Digg or Reddit. The creators have said so themselves.
How closely to a pre-existing design or market space does a product need to be before it offends you? Do you have a methodology to measure this?
How much time have you spent trying to woo venture capital? In my experience, one of the first questions I get hit with is "is there anyone else doing something similar?" If the answer is no, this is a red flag.
A typical and expected elevator pitch is "its like X but for Y". Hybridization is the game here. It is common and quite acceptable to say "its like X but for China".
The creator of this new product did change something...something critical... "its like StackOverflow but for China".