It doesn't matter if it's a parallel or series hybrid. The electric motor does the most work in stop and go traffic, and thats what also hurts your engine the most. The electric motor allows the gas engine to not have to stress itself as much, and run in much more optimal load ranges.

Gaskets and seals almost never have change intervals, it's replace them when they leak. Air filters are $30 and take 10 minutes to change so the labor rate is stupid cheap for those. Synthetic oil changes aren't that expensive, and last a lot longer than most people think. Many German (regular gas) cars suggest 1-2 year and 10-15k mile intervals for their oil changes, and even dealers will do those for under $100. In 5 years I've spent less than $1500 in maintenance on my regular ass gas Outback, and that's doing work way ahead of schedule, not waiting until Subarus prescribed times. Maintenance costs are not that big of a concern for new gas cars.

What holds people back from EVs is range anxiety. A phev gives them exactly what they want.