I think you're spot on with your assessment that staff continuity is a vital part to program consistency (sans Alabama). I think there are a few different reason for the staff consistency up at Clemson.
There's no doubt that the way they pay their assistants up there is a big part, but it's definitely not the only reason given that other schools have no doubt offered some of them comparable salaries to leave.
Some of the hottest names there are their OC's Tony Elliott and Jeff Scott. Both of those guys are Clemson alums with long histories at the school, so it would probably take a perfect opportunity for them to leave. A lateral move is probably unlikely for them and given that they are fairly young and have kids in school in the area it probably makes it even less likely. That's not to say that they wouldn't eventually leave for a HC job somewhere, but it would have to be a perfect fit.
Duplicating that formula with two OC's that could prove to be such great hires at most schools could be difficult given how well Scott and Elliott have performed since being promoted to replace Chad Morris. I don't think many people including Clemson fans would have predicted that their offense would actually improve in many areas after losing Chad Morris.
With Venables I think it is a combination of a few things also. First, they have made him one of the highest paid DC's in the country for several years now. Also, he now has a son that is playing at Clemson. For those reasons I don't think he would want to make a lateral move. He seems to be the type of guy that remains loyal to a program for the long term as evidenced by his long tenure at OU and now Clemson. I believe he only left OU because Bob Stoops brought his brother back in to be co-DC. Finally, Venables seems to be one of the rare coaches that is perfectly content remaining at the coordinator level instead of becoming a HC. He could possibly move back to his alma mater when Bill Snyder finally retires, but outside of that I don't think he'll be leaving for at least a few more years.
I think they have had some turnover with their other assistants. I know they lost a DE and DT coach just a couple years ago. Their QB coach is their former QB Brandon Streeter whom I haven't heard mentioned as a candidate anywhere else. I'm not sure if Robbie Caldwell has been a candidate anywhere either.
