I think that it's a good reminder that all the sentiment in the world is meaningless in the face of changing ownership and/or business realities. See also Instapaper + Pinterest.
Edit - Also a reminder to founders: If you want your vision for the company to survive, don't sell it!
Founders that sell are very much aware of this fact. If they're selling it's either because they have no choice, or because they don't believe in said vision. In the end, unless you have a strong contract that protects users with the threat of a fork, like being based on a distributed open protocol, or an open source license, it's all just bullshit and marketing, whereas aligning with your users interests is only temporary.
I also think there's an inherent lesson for users here, more than it is for founders: don't trust startups, most of them won't survive and won't have the decency to die either, preferring instead to sell your account and data to the highest bidder.
> If they're selling it's either because they have no choice, or because they don't believe in said vision.
Or just because the price is right. Some may believe that they can do something even greater with the money, and some simply realize that a lot of money is the more attractive option for them. The latter may even have faith that the purchaser will keep the vision alive (and most will be disappointed in that respect).
Edit - Also a reminder to founders: If you want your vision for the company to survive, don't sell it!