So... If you read the article about the Bills roster revealing a lot about their intent to run more 12 personell due to more defenses utilizing the 2-high shell which is designed to take away the deeper passes, then this signing makes a little more sense.
Should the Rams find themselves running into a lot of match-ups against 12 personell, then Gervase is likely better in coverage than the other options.
While I love the addition of Bobby Wagner, his coverage skills are not elite. I'm not saying BW isn't a big improvement over Reeder, he is. But if you are purely looking at who would likely cover a TE or RB coming out of the backfield better, between BW and JG, then JG is probably the choice. Heck, Ernest Jones is probably better in coverage, too.
Personally, I hope we don't have the Rams matched up a ton against 12 personnel because that may limit the amount of time BW is on the field.
This is NOT A KNOCK AGAINST HAVING BOBBY WAGNER ON THIS TEAM. I think BW adds a lot. It is simply a possible reason the Rams decided to keep Gervase on the 53 (for now anyway).