It may be that the higher cost is a much better value because the painting contractor is very thorough and attends to a lot of details that the other contractors miss or ignore.
Obviously using high end materials can cost $20-$40 more per gallon and is worth it because of the longevity that they are forward. He may be using caulk which is the best on the market and cost $11 per tube. And caulking, being such a critical function is well worth the cost as it helps prevent rotting wood. There are some specialty materials he may be using such as special metal roof paints that last twice as long as a regular house paint. He may be using an $80 per gallon oil base metal paint for the iron porch railings. Marine varnish is up to $100 per gallon for the highest quality. There are also special acrylics that are purchased to use on coach lamps and chimney caps. He might have higher skilled men that are paid better. All these things amount to great longevity.
He may be doing other things such as and washing all the exterior window, cleaning gutters, caulking the coach lamps at the brick or siding and may be just very detailed knowing that these are trouble spots and need attention.
The high estimate is often times because they have paid very thorough attention to the details of the carpentry that is required to replacwe all the rotten wood. A visual inspection of the carpentry will miss a lot of areas of rot. He knows that if these are not attended to the homeowner will be replacing rotten wood and painting again the next year. It requires a physical inspection.
All these things contribute to a comparatively higher estimate but is well worth the money to make sure the house painting has great longevity and potential problem areas are attended to.