I agree that the barrier to entry is lower now.

However, I think one of the reasons for their success is due to their roots - The Point, the startup using collective power to help people deal with local issues. Groupon's founder once said, "None of us would work here if it were only about selling stuff at a discount—ultimately, we're trying to give people an excuse to get out of the house and enjoy life."

I think a successful company needs to have a corporate mission that is bigger than making a profit. I believe their roots help them build a strong brand and user base, which is a very strong barrier to entry.