Gmail is a significant enough profit center that it's unlikely to ever be under threat. Reader didn't directly contribute to the bottom line (and arguably led to fewer ad views).
Google knew it could kill Reader because a low friction transition was possible. Killing Gmail would register in the stock price.
It is a lot easier for people to protest by not doing anything than actually putting effort into it. Switching from Gmail to some other provider involves a lot of friction. Not using a newly released product (assuming this will be one) is fairly easy.
Such things are hard to judge. I have a feeling that a lot of people (a lot more than usual anyway) have recently transferred their email from an @gmail.com address to a Google hosted custom domain.
On the other hand, with Google Apps you can actually be a paying customer. Maybe the fear factor just isn't there.