Why do you think that? I would think Beltre would sail in on the first ballot irrespective of Rolen's enshrinement. He's one of the best half-dozen or so 3Bs ever. Couple of further notes:
A. I'm very happy for Rolen, as I watched closely his formative years. I harbor no ill will for him wanting to leave; Bowa was a total prick to him.
B. With Rolen making it in on the 7th try, I think that makes sense. And it's too bad that their careers didn't start 20 years later, where a larger group of voters better understand value, because Bobby Grich would be heading in on the 7th or so, and Whitaker would've flown in on the first try.
C. Rolen taking 7 tries illustrates the difficulty for 3B in general, as it is the least represented position by far. I think it's partially because where it is on the continuum:
SS C 2B CF 3B RF LF 1B DH
So the farther left on the continuum, defense is stressed, where on the farther on the right, hitting is stressed. Which helps explain why someone like Keith Hernandez, regarded as among the best defensive 1Bs ever, couldn't sniff (no pun intended) enshrinement. But there's not really an archetype for what an HOF 3B is. Because we don't necessarily see it as a defense-first position nor an offense-first position, the really good ones seem to fall through the cracks. Which is too bad. There's no reason Ron Santo, who was around a top 10 3B, had to wait until the veterans committee.
D. I'm cool with Andruw in there as a high-peak guy.