Yep: beta updates never come out on Steam, ever. However the in-game updater is perfectly compatible with Steam and so you can have it right now if you like (judging by the multiplayer server listings most people are opting for that).
Once we pass a certain point and polish up this batch of betas, we'll do a new official build and that will replace the current official build on Steam, in installers throughout the web, and so forth. Next official build might be in 3-4 weeks, we'll see. Usually they'll be more like every 2 months, but for the first one or two we'll probably move faster to turn the post-release betas into an official.