“As Pete Cashmore on Mashable says, it’s because the subscriber numbers don’t reflect actual readership. The people who subscribed may not even be aware that they are subscribed. Or put another way, we haven’t learned yet how to measure what’s valuable, we only have the crudest ways to measure value, so crude as to be meaningless.”
Dave is, of course, correct. However, this is exactly the same situation as print magazines, which have massaged subscriber numbers for decades – adding to them using “bulk” copies (mailed in large numbers to companies), and other tactics.