From what I heard, his "groundwork" was a terrible mess of spaghetti code that was awfully hard to work with. Most likely the only thing he left behind was the IP and fan base.
I meant more the initial marketing and community involvement that helped the game get popular in the first place. Much as it pains me to say it as a developer, code quality isn't everything...
You're right. I'm positive that every time a large company acquires a small one, it's because of their community and IP. Code is easily rewritten, and startups aren't making breakthroughs in algorithms. It's not like microsoft didn't have engineers capable of making a minecraft clone. They didn't have the rights to do so.
If you go look at my githb account you will see lots of spaghetti code that will never be sold for $2.5 billion ;-) It doesn't matter how poor the code was, it was incredibly valuable before anyone else joined the company.