I think itīs all about margins. Even though the engine is capable of producing 280hp, not much of the rest of car stands those kind of powers for any longer time. The cars are designed to last at least 15 years reaching 300000miles with ease. 185hp or maybe 200 as in the 9-3Sport 1999, is a maximum while retaining the life span.
If SAAB had decided to go with 3" exhaust and 250hp on the ng900 and 9-3, they would have had a lot of those cars filling up the garages with warranty replacements of trannys, clutches turbos and not to forget all the badwill from people killing themselfes due to low-performance road holding.
All these things can be adressed, yes, but at a cost. Adding $5000 in aftermarket parts on a new car directly from SAAB (and by SAAB) would raise the price of a new car with a _lot_ more. And still you canīt be sure that the engine will hold for hours and hours of WOT at a 120F in some distant gulf country.
Then why did they choose those injectors? Probably due to a good deal, and that they can use the same injectors on all cars and so on, logistics is also a way to increase revenue