If you're already running OS X Yosemite gold master release candidate 3 (GM 3) or public beta 6 (PB 6), you won't need to update to the final release version in the Mac App Store (MAS). While there are minor differences in build numbers between the versions, Apple is considering both GM 3 and PB 6 as "final" and not offering the MAS version to anyone with either of them already installed.
Yes, if you're really fussy about your binary bits, you can download the final version from the MAS and run the installer anyway, but it's more gigabytes to download for very little difference, so only true completion-ists should even think about considering it.
Otherwise, whenever Apple releases the next point update — OS X 10.10.x — you'll get it same as everyone else, and be on the same build as everyone else going forward.
If you're on GM 3 or PB 6 and still debating whether or not to manually do the upgrade, let me know what you decide!