The funny thing about that article is I was literally in the process of writing a near-duplicate content blog entry on the very same subject when I saw that one.
As for why we're seeing the records, I don't think it's drug related at all. Swimming has as deep a drug history as track. I think the frequency of records is talent related along with improvements in sport technology (improved swim suits, pools, lane lines, etc.), training methods (swim training was VERY old school until recently), and techniques (several techniques have come along over the past 20 years in swimming which directly lead to WRs).