That doesn't happen from not logging in, that happens from not having a SC2 license registered with your bnet account. Sounds like you somehow bought the game but then installed the free version of SC2?
It does, unfortunately, happen from not logging in as well. If you go over about a month without logging in, it will essentially treat your install as being a trial account as it can't verify that you have any higher level. Having being stung by it a couple of times, I now make sure I log in just before I take my laptop somewhere that might leave me without an internet connection.
My Heart of the Swarm disk never even made it into the drive. The game was already patched to the latest Wings of Liberty patch, which apparently includes all of the needed files for HotS. So once I added the HotS key to my bnet account, I just needed to log in with no additional downloading.