Thankfully that kind of thinking has changed in today's tech world.
Outside of online businesses, do you really see a lot of young CEOs?
Look back at the dot-com bust. There were a lot of businesses that started and failed because they didn't have experience in the distribution of physical product, etc. (Peapod and Pets.com come to mind.)
If you're making stuff, then you've potentially got more fixed costs than you do than if you're running a software business. Those fixed costs alone can put you under.
In any case, I think Steve was too busy in those days being a micromanager for the Macintosh team to even think about running the company. Don't forget he spent a lot of time alienating the Apple ][ team, who was responsible for most of the company's revenue at the time.
Getting fired, running a relatively unsuccessful company (NeXT) and nurturing a company into massive success (Pixar) probably gave him more valuable experience than if he had somehow managed to stay at Apple in the first place. And for all we know, the world would have never had the opportunity to see Toy Story or the Incredibles. Clearly, I see Job's firing from Apple as a win for the world. ;)
Also keep in mind that while at NeXT, they switched from a hardware and software company to a software company (and so did Be, which was the other company Apple considered buying).
I don't understand your final sentence though... To whom are you referring when you say "They switched from being a H/w S/w company to a S/w company" ?
I thought that both NeXT and Apple continued to produce their own machines and software.