He's been in the bigs for 4 years. If they don't know what he can do by now, then it's not just the players that they should be looking at!
I think his problems to start the year caught them very off guard. The rationale up to that point and perhaps even now is that when Burke is given a regular full-time job at one position he can hit well. They'll point to the second half of 05 when he was essentially given LF, and his last full season at AAA when he had a career year at NO. I believe that they believe that if he's given 2b full-time his bat will be acceptable only now that belief is tinged with a little doubt thanks to his flop at the plate to start this year.
Also, from Purp's statements, there isn't much in the minors right now to reasonably callup. McLemore would be fine. The rest of the RR pitchers haven't exactly been lighting it up. I suppose they could recall Albers. Patton is better than AA, but he'd get torched by mlb hitters. He hasn't been consistent this year, but his stuff is good enough to get AA hitters out. His lack of consistency would get exploited by mlb hitters. Unless, he goes PENCE!!! and suddenly figures things out. IOW, if Purp is going to make changes to the 25-man to improve the club this year it'll come via trade.