Depreciation for the 737-500

Depreciation for the 737-500 looks rather low compared to the -300 and -400.

This means that as the aircraft ages it gets comparatively expensive compared to the larger -400:

737-300 Depreciation Rate: 0.080, Base Price: 44,000,000, after 10 years: 20,380,513
737-400 Depreciation Rate: 0.075, Base Price: 48,900,000, after 10 years: 23,725,983
737-500 Depreciation Rate: 0.040, Base Price: 42,000,000, after 10 years: 28,373,695

(after 10 years is a rough estimate, ignoring used plane fees, discount when bought in bulk etc)

This is most obviously an issue in world S2, where there is no leasing.