Considering they also rejected Google's offer, I'd say there was more to it than Yahoo's past failures.
You are right. However, I don't think Yahoo's track record in integrating acquired companies helped them at all. Google is perceived as an innovative company where Yahoo seems to follow the leader.
Yahoo cares about products that make revenue, which is why it is dropping things like delicious. I think Groupon would have had a different priority within the company.