Sorry, but I've had both many times over and this is not very accurate. The transmissions fail somewhat unpredictably, turbo or not, and there is nothing you can do about it really. I've seen turbos with original trannys go 200,000 miles. I've seen N/As with trannys that didn't make it to 100,000 miles and vice-versa. I have one from an '89 N/A with 110,000 miles sitting in my basement with a broken 5th gear syncro spring which then chewed up the gear teeth and it's far from the first one I've seen. I'm not sure what others have experienced, but from my own experiences and junkyard observations (which are too numerous to count), the trannys last for around 100,00-150,000 miles on average be it auto, manual, turbo or N/A. The exact failure is not always the same though.
As far as engines go, the turbo is no more difficult to learn than the N/A. If you go back to 8 valves, they are nearly identical with the only real addition being the turbo itself (and APC on later 8 valves). In fact, one can bolt on the turbo specific components and run a nice 5 psi boost reliably on an 8 valve N/A compression engine, sans APC (I've done it and it was an absolute pleasure to drive). The 16 vavle is similar in that there are unique systems to each which adds or subtracts complexity, making them about equal. The turbo adds the APC system, but removes the EZK system in favor of a simple mechanical distributor and no crank sensor (I think everyone would rather deal with a hall sensor than a crank sensor). The turbo itself, the intake piping and the boost bypass valve are the only real additions and there's nothing complicated about any of those parts.
For me, after having owned MANY Saabs of different configurations, I'd get a turbo every time. That is, of course, assuming all things are otherwise approximately equal in terms of condition. If you're comparing an N/A with 80,000 miles to a turbo with 220,00 miles, there is an obvious advantage to a car with fewer miles typically. It is quite apparent, when you take an N/A and turn the exact same car into a turbo, just how much better these cars are with some boost. If you have an N/A, I highly recommend learning enough about the turbo system to add it. An N/A with 5psi of boost is peppy off boost and has just enough extra go on boost to do 75mph over a pass at altitude in 5th gear instead of 4th.
The cool thing about Saabs, in my opinion, is the fact that with junkyard parts readily available and often in excellent working condition, you are never stuck with a particular engine configuration if you don't want it. While it's always best to buy what you want upfront, in the absense of that possiblility there is the opportunity to change what you've got INTO what you want. Saab parts just bolt together and play very nicely with each other. You don't even have to stick with the older engine management, since T5 is available in the junkyard to install as well bringing a c900 up to date with currently available ignition components which can be bought new (try finding a new c900 distributor these days).