Actually, no, apparently not. It seems that there was inside information going in both directions between Bukkit and Mojang, and in fact individual coders were working both sides of the fence. Bukkit was the most successful modding framework for a reason.
I don't want to drag up the entire war again, but there were some coders who were absolutely committed to the game, and who had back channel connections to Mojang.
It really was an important part of the Minecraft server explosion, because Vanilla Minecraft has absolutely no in game sense of ownership or permission structure, and without the various modding frameworks (of which bukkit was the most popular) a public server is literally (in the literal sense) impossible to keep playable.
Yes there are mods that directly patch the Minecraft libraries, but they are a nightmare for server admins, because they break each other and are seemingly broken by every Minecraft upgrade. It is much less work for devs, and less headaches for admins when mods are written against a common framework.
This is why modders were excited when Mojang announced the upcoming API, and some very good mods actually were abandoned, since the API was coming "soon" and the modders didn't want to keep rewriting for every version and decided to wait for the API. And wait.... and wait....
My honest opinion is that Notch got bored. If you look at his coding habits before Minecraft he has churned out a lot of code, much of it quickly. He loves the hack fest and coding competition environment, I think doing one thing for more than a year, and being responsible for a suddenly large business operation got tiresome. If I was in his shoes, and had the money he has, I probably would have responded similarly, except for the Microsoft part.
But I am afraid Minecraft without Notch is like Apple without Jobs. A large part of the success is dependent on the vision of one individual. I expect Minecraft will start to lose focus in the same way I think Apple already has started, not because of lack of good people, but because an autocratic dictator is always the most efficient leadership toward a specific goal.