If 30 days was not sufficient, then they should not have set a 30 day minimum. It's their number, not yours. I don't think you should have any qualms about it.
Since you're not looking to work in the industry again, why worry? As some others have said in the past, with an extended notice, the company may just drag their feet. You are giving them some motivation to get on with it. You're doing them a favor!
If you have people there that you feel a personal connection to that might need to put in really long hours if you depart in 30 days, or a strong loyalty to the company, you might consider (but don't tell them) extending for 15 or 30 days past the original 30. But only if they were diligent in finding a replacement for you in those first 30. If an extension just allows them to drag their feet some more, fuggetaboudit, get on with your life.
The business owners I know who have sold their companies typically are put on staff for a year to help with the transition, but it usually amounts to very little time (like being 'on retainer'). I know of one case where there was so much disagreement on where to take the company, the new owners just bought the previous owner out of the remainder of his contract.
I'd give a little waiting period on those bonuses, then go on and enjoy your new life! A few weeks (days?) in, I'll wager you will be wondering why you were even concerned about any of this!
edit/add: With the other execs who gave a year or more, it might have been an ego thing. "They can't get by w/o me! I'm too important! They will need at least a year to find someone even close to my ability! They might have to hire two or three people to replace me!"
-ERD50