>There have been only 3 successful open source companies ever: MySQL, Jboss, and Redhat
See now, there's just no reason to go around saying things like that. Even if that were true (it's not), how would you know that it's true? Do you have a complete database of profitable businesses in your head? I doubt it. A significant number of open source companies are privately held, and there's really no telling how successful they are.
Anyway, right off the bat, you missed Mozilla Corporation.
Beyond that, the question of whether a company that does nothing but develop FOSS is irrelevant. The important question is whether developing FOSS can be a major part of a successful business strategy. You might start by asking Google and Apple.
Mozilla Foundation is non-profit. Mozilla Corporation is for-profit, and makes most of its revenue by selling the default search engine slot in Firefox to Google.
>I think the companies listed only develop Open Source software and sell services.
That's true, but I think it's looking at the situation completely wrong. It's sort of like saying that making left shoes is unprofitable because there are so few successful businesses that exclusively manufacture left shoes.