Actually, I will just assume you are referring to Hollinger's Rebounding Rate. Where Rondo is tied for 4th among PGs at 7.2, and Rose and Williams are 18th and 19th at 6.3 and 6.2.
This is an interesting stat, but once again, I don't think it takes into account the guys these guys were playing with.
Rondo was playing on a team that really struggled to rebound. Other than KG, they had no other above average rebounders (and KG is certainly not at the top of the league), and this left a lot of extra rebounds for Rondo to grab. Rose on the other hand played with Noah and Boozer, two consistently excellent rebounders, as well as several other very strong rebounders in Asik, Gibson, and Deng.
Williams had a similar situation, where he spent half of the season with Al Jefferson and Paul Millsap gobbling up all of the rebounds, and then spent the second half with Kris Humphries, who was on a mission to get paid and averaged more rebounds in the month of March than KG and any of the C's centers combined (14.

. So, there just were not as many rebounds available to grab.
Furthermore, when you look into the stats more closely, particularly compared with Williams, you see that Rondo's rebounding rate is largely so high because of an inordinately high number of offensive rebounds. Williams actually has a higher defensive rebounding rate than Rondo, and I would argue that Rondo's offensive rebounds can be directly attributed to defenses completely ignoring him due to his ineffectiveness offensively, rather than him actually being a superior rebounder.