The zeitgeist in the short time since Kenny Britt's signing is that it changes the draft, since it's obviously a move that precludes the Rams selecting another WR. Not to say that it's entirely implausible for the Rams not to select a WR, but there are bigger reasons why the move is entirely irrelevant to our draft situation.
After the Steve Smith debacle of two years ago, Rams fans are justified in being cautious; however, Britt is a good signing for the price we paid. It takes up a minimum of cap space on a player with proven potential, but a shaky future.
The best way to look at Kenny Britt is as an insurance policy. The Rams don't need him to make 100 catches this year; we've already got our five starters who can at least move the ball downfield as long as the run game is ticking along. What he provides is depth. Say Quick or Givens goes down, Britt fills in instead of the lukewarm backups we have like Veltung. Just like Kellen Clemens was for Sam Bradford, Britt is an adequate backup who means that our whole season doesn't go down the tubes just because a starter is injured.
To my ultimate point, having Britt doesn't change anything in the draft because no one in the front office expects him to play an integral role in this offense. Snead and Fisher think our current five are already "good enough", so if they select another WR, they'll do it because his talent is too great to pass up, not because they "need" another WR. Britt doesn't that calculus.