This thread sure brings back my Epson 4000 days. (Maybe it's the 4xxx series printers.) I went through TONS of ink with cleaning cycles. An Epson technician with whom I spoke suggested that the problem could be air leaks into the ink lines.
Anyway, It became just too expensive to continue with that printer. So, I purchased a 3880, and it's been great. I've left the 3880 unused for months, and I've never had a problem. Others have the same experience.
Hmmm. This makes me ponder whether Epson is leaving technology out of the 4900 that they've included in the 3880??? They make a lot of money from ink clogs. Does it make sense that there would be such a huge difference (regarding ink clogs) between the two printers?