Sorry, I'll have to very strongly disagree on that one. If, for example, you conduct a public opinion poll in the United States, then all that matters is the size of the sample and your method of selecting the sample. If those are both adequate, then you can draw conclusions (with margins of error) about the entire population. Furthermore, you can repeat the same poll at different points in time and draw conclusions on the changes that you observe. What's happening here is different. Your population is all programmers. Of that, a subset is taken, namely, the set of all Dr. Dobbs readers. From that subset, you take your sample. I trust that the size of your sample and the method of taking it are fine. But we don't know if the subset from which your sample is taken is sufficiently random, and we don't know if and how it changes over time.

In short, you cannot draw conclusions about the entire population if your sample is taken from a subset that does not qualify as a random sample. That problem is very definitely not "inherent in all surveys," as you claim.