See a few thoughts (in reverse chronological order) below.
I think Kevin, M.D. was right about Twitter being easier to adopt than RSS for the non-tech crowd. Note: there is nothing wrong with "crowd" -- Wikipedia is based on the "wisdom of crowds."
AllergyNotes In summary, the trend seems to be that many popular bloggers have more Twitter than RSS subscribers nowadays.
AllergyNotes It could be the personal interaction that makes Twitter more interesting than RSS or the need to "follow" somebody as a guide and example.
Twitter as RSS Reader? Will You Switch from Google Reader to Twitter?
Will Twitter Replace RSS?. TwiTip.
"Rest in Peace, RSS" by Steve Gillmor who uses Twitter instead, 2009.