In Dark Heresy the maximum bonus that could be applied to a roll was +/- 30.

In the Rogue Trader preview edition (Forsaken Bounty) that bonus was increased to +/- 60.

I can't find this rule in the released RT manual. Has it now been dropped, or do you think it's an ommision?

The DH errata opened it to +-60

So the general view is a typo in the printed RT book. (The box out for combining modifiers isn't included).

Nope, my RT book say -60 to +60. I don't hve it in front of me, but I know for sure it says that.