Well, Robles does have one more SB, and Robles has an OBP of .336 versus .306 for Taylor. And he's cheaper.
He's also slugging nearly 100 points less. There's not a huge gap between the two right now, really: Taylor popped a couple over the fence on opening day and has 3 homers since. But that's still 3 more than Robles has, which explains the slugging gap.
If you're going to hit zero home runs, you need to get on more and steal more than Robles does. There are only seven players right now with more PAs than Robles and zero homers, and not surprisingly most of them (David Fletcher, Elvis Andrus, Leury Garcia, Myles Straw) have been absolute dead weights on their team's offenses. Taylor hasn't been.
