The engine could be sludged in spite of the oil change intervals, which appear to vary quite a bit. An 11 year old car with 135k miles points to about 10ish thousand miles a year and if this driving consists of mostly city driving then sludge could be a very real issue.
Changing an oil pump is generally a misguided effort to cure the problem. You say the oil light came on and when this happens the motor is usually dead meat to some degree. This means the crank bearings are being scrubbed away and this happens very quickly. Once that occurs oil pressure will dwindle to nothing, or near nothing, and the need for a new engine arises.
What would I do? Drop the oil pan, check the oil pump pickup screen for oil sludging/coking and remove a few bearing caps to verify crank bearing wear. Any sludging or coking rules out the meticulously maintained part of this.