Those aren't builds they are optional Class Features, there is a build for most Class Features, but you are not forced to take a build, just a particular class feature.
The line from class feature->build is pretty straight. When powers play off of class features and are much more useful with them than without them, not taking them requires a willful disregard of your characters ability to function.
It would be like choosing 2-weapon ranger, then only taking ranged Encounter and Daily powers. I suppose that the rules don't STOP you, but why would you? You can't build an (effective) mixed range/melee ranger; pick one. (with Martial Power, judging from what's been revealed, the choice becomes "Pick one of three", which is notably superior; I have no doubt it will, someday, be "Pick one of five" or "one of six". Point is, you make your pick, and then you're 90% done with choices for your character. Race, Class, Build, GO! This may be considered by many to be a feature, not a bug, and I do understand their arguments; what I don't understand is why they insist on trying to DENY it, instead of trying to SELL people on it as a Good Thing.)