NSB GRoup - official thread

i cant tell you specifically about NSB but

software houses gets around 15%, possibly more, of the LIST price of the software as maintenance. thats the cach cow side of the software business and what values it once it comes to market. but they do have to provide service for that. the better the software is designed and written, the less they have to spend. then they get fees for additional customisation work

note that its the list price, not the selling price (which may include customisation work) unless they do long term maintenance deals