Back in the day singles were almost always mono. The added echo and Wah-Wha effect would of been done to add some depth to the mono recordings and make them better stand out on AM radio. The same effects used to excess on album stereo versions I suspect would have been a bit over the top! Singles were often shortened as well, less than three minutes, I suppose that the general audience had a short attention span.
It's always nice to have both versions, frustrating that you rarely hear the original singles played on radio anymore, always the album version, most noticable if the track is much longer than the single was.
