Well to release gears to a application like reader or docs is easy cause your userbase is small. Gmail is a HUGE product with thousands of users and to even release something like that to labs you need complete protection of not only the data but also security for your DBs.
Reader and Docs were simply there to ensure the safety, if they went down due to security issues not that many people would be concerned.
Google's audience for reader and docs are in the millions and could hardly be described as "small", just like Gmail has a lot more than "thousands" of users :)
You understood my point :) But gmail vastly outnumbers docs and reader in both security and scale.
Thousands of emails and contacts with personal information. Docs and Reader doesn't need to store the contacts or emails of the user. Docs stores data and reader stores stores.
While I agree with you about Reader, I doubt the security implications for Gmail are much more severe than for Docs, because so many businesses are using Docs through Google Apps, and you know they're storing sensitive info on there. One breach and it's over.
Also, I think with Gmail its a bit harder to decide how much to store on your local drive. I believe Reader just stores your unread stuff, but with email you often want to search or reference old messages, so its a substantially more complicated thing to deal with UI-wise.
Reader and Docs were simply there to ensure the safety, if they went down due to security issues not that many people would be concerned.