Effective research needs to be based on correct selection of clients - ie the demographic surveyed must be representative of the overall population it purports to represent. If your demographic has already responded in enough numbers then your survey experience will be terminated when you respond to that question. Nothing personal.
This is the first time I've ever heard an argument for statistics been made better through less collection of data. Now I'm no statistician, but I am someone who works with vast quantities of data (software developer as a result I've written more than my fair share of reports). When one particular group has the ability to overly influence the result (and that in itself is data) there are formulas which can be applied to level out the results so no one particular demographic does overly influence the results.
Furthermore since the processing of data takes no more than a few minutes even for the largest of data sets (I've played around with software which could easily analyze a response from every single person in Australia if you managed to get every single person to respond) it's not like in the old days where paper based survey's involved someone physically eyeballing a response. Even if the response included a written component, that's easy enough to analyze these days as well.
Besides, even if they had received enough data from my age group and there is a valid statistical reason why not to include more data in the research, then why not collect the data anyway for 2 reasons.
1. I'd never know if the data wasn't used. Seriously how would I ever find out that my data didn't go into the survey results? Am I going to be the only one in 10,000 people whom awards a 7 in an out of 10 question that the results make it obvious my data wasn't used?
2. It'd give me the warm fuzzy feeling that QF was actually listening, I've decide to spend time giving them feedback, and I'll assume that on clicking the submit button it'll actually get what I've told them.