What exactly is "Getting their rhythm back?"

Players get hurt. They come back. They do a minor league assignment. Then they get put on the major league team. And then the announcers say that they aren't hitting because they need to "get their rhythm back."

So, I'm wondering,

1. How long does this cop out last, and
2. Why the heck are they called up from their minor league assignment if they still need to "get their rhythm back?"

If we have to wait 20 at-bats for Garret Anderson or Maicer Izturis or Reggie Willits or Casey Kotchman to get their rhythm back, why don't we have Nathan Haynes, Robb Quinlan or Kendry Morales go 5-for-20?

To see if there is any validity to my point, I'm going to look at Angels players this year coming back from an injury.

Chone Figgins. He broke a finger in spring training and came back late in April. He didn't get on track until June. By the end of May he was hitting .133 (12-for-90).
Verdict: Spent 4 days with Salt Lake. Wound up taking 90 at-bats to get his rhtyhm back.

Casey Kotchman. Kotchman missed 9 days due to a concussion. He went 0-for-19 and then hit a home run. But he still isn't back. Including today's 0-for-3, he is 2-for-31 since coming back.
Verdict: No rehab in the minors. He's still not ready.

Garret Anderson. GA has been out twice this season already with leg problems. He hit .265 in April and then missed all of May. He came back to hit .265 in the first two weeks of June so it seems he was ready. He got re-injured and missed another two weeks and is 3-for-10 in his return.
Verdict: GA appeared in 6 minor league games. Love him or hate him, GA is smooth.

Maicer Izturis. Izturis returned this week after a 6-week layoff. He has hit 2-for-6 so far and seems ready.
Verdict: Spent 12 games in the Minors. Has his rhythm.

Howie Kendrick. Howie was hitting .327 when he was hit by a pitch on his hand. He missed 5 weeks and came back with a 5-for-40 slump. His average bottomed out at .236, but is now up to .295.
Verdict: Spent 7 games at Salt Lake. Needed more rehab.

Reggie Willits. Reggie just missed a week with a bruised knee. In his two games back he is 0-for-7.
Verdict: Didn't rehab in the minors. Too early to tell, but I'd sure prefer a 2-for-7.

Of the six hitters who have been out for a week or longer this year, 2 didn't rehab in the minors - Kotchman & Willits. Unfortunately it seems that both of them should have spent some time rehabbing.

Of the remaining four players, two players needed a longer rehab. Figgins spent 4 days in the minors and needed more. Howie spent a week with Salt Lake but that wasn't enough.

GA showed that he is a true veteran. He spent six days with Rancho Cucamonga and was ready. Maicer isn't a veteran, but the Angels took their time bringing him back and he looks ready.

I guess I'd like to see players spend more time in the minors rehabbing. I would think that their "rhythm" could come back in single A as easily as the Major leagues.

Then again, there are always alternative methods. Maybe they need to watch "How Stella Got Her Groove Back." Or, if you ask Mark Grace or Jim Rome, maybe they need a Slumpbuster.

If you ask me, an extra week of buying minor leaguers dinner is the way to go.