Third party apps are HUGE in the smart phone industry. And, I honestly believe it sways users from one phone to another. For instance I love BB but their apps are horrible, so I use my iPhone more. I also know many people who feel the same way. Smart phones are not just voice phones anymore, apps are a major reason why people purchase smart phones.
There needs to be a very strong, stable, and smooth Android Market for apps for this system to succeed.