Terran planets have a maximum of 24 logistics slots, asteroids 12, desert planets 36, volcanic and ice planets 20.

TEC can research a tech to increase the logistics capacity across the board for all planet types by I believe 4.

However, as labs take up 4 slots a piece, the answer to your question is effectively yes, this is normal.  You're going to need to spread out your labs amongst your worlds, if you want to build anything else at them.

Thnks for the info guys --- although at first it seems there should be at least a few more slots, I would imagine the devs thinking was that it would add to the strategy of the game as you have to really think of what you want to build before you make a decision.

Which is why, when attacking an enemy, always prioritize planets above asteroids etc, for the logistics slots. Sometimes (esp. later stage game), you can even completely bypass an enemy asteroid for a planet. The loss of whatever things (labs, factories) in those logistics slots you razed from the planet are not easily replaced if the enemy does not have enough logistics slots elsewhere, and so, the effect on their ability to respond is quite significant for a long time.