Remember a few years back when the Spurs made a hard run after Jason Kidd because of Tony Parker's inconsistency in the playoffs?
That's where I see Rondo today. Flashes of brilliance, followed by periods in which he looks completely overwhelmed. That's OK, that's really pretty common for a young player.
Rondo's not having very many good road games, but neither is the team as a whole. Let's not overreact, let's look at the body of what he's done this year and make some reasonable projections about how and where he might continue to improve his game. He's gone from a complete nonshooter to having an OK outside shot; if he improves just a bit more (and keeps his confidence up), this won't really be a weakness anymore. We know he's got the speed and quickness, and he GENERALLY makes pretty good decisions with the ball (less so when facing the pressures of playing on the road). This is something that you would completely expect to improve with some experience.
So, no... Rondo's the starter for the foreseeable future, and that's a very, very good thing for the Boston Celtics.