Steez is right.
The labels go a bit far in the claims made in my opinion. What those batteries have is a moisture entrapment cap. The cap is made so that it attempts to condense "boil-off" moisture and drip it back into the battery. This helps reduce the loss of water, but it does not stop it. This is why the battery doesn't need distilled water replenishment every time it is charged - but it will eventually need it. This is why informed lead-acid battery owners check their battery level.
Make sure you understand what "top off" means for a battery as some people have thought it is meant literally, so they grossly overfilled a battery. There are some pricey systems that will fill each cell correctly from a common water supply tube. I have one to try, but haven't installed it yet. For my 3 TM batteries, it cost about $100, but should ease and improve maintenance.
If you want some insight into battery condition, get a good battery hydrometer and use it when you have those caps off to check the electrolyte level.