Or, you know, it could be the fact that Sweden's industrial capacity survived WWII largely intact and so the country in general was better positioned than the rest of Europe to make money.
The same thing helped out post-war America as well. Was isn't good for the economy on average, but when all of your industrialized competitors get bombs dropped all over them and/or occupied your relative advantage in manufactured goods goes way up.
This theory doesn't hold up at all. Germany nearly flattened, and yet, they had the Wirtschaftswunder ( https://en.wikipedia.org/wiki/Wirtschaftswunder ). In fact, it wasn't just that Germany was bombed, but after the war their machinery and even their top talent were ruthlessly pillaged by both the West and the Soviets. And yet, Germany emerged just as well (or better by some measures) industrially than Sweden or the US.
If you want more counter-examples, look to Japan, nothern Italy, or Austria, whose industrial capacity and economy became exceedingly powerful after the war.
A lot has to do with the stability of your society; as long as your government and talent is relatively intact, you can rebuild quite quickly even from extreme catastrophes. Its only when you start "liquidating" the intelligentsia (Cambodia, Soviet purges) where you begin to take steps back, or maybe a prolonged multi-decade war or colonial occupation (Afghanistan, India).
I would wonder if the Marshall Plan didn't contribute greatly to the post-war success of Western Europe (as was the intention of the program). A cursory glance over the Effects section of the Wikipedia page shows that the effects of the plan greatly increased Western Europe's industrial and agricultural standing.
It sped things up, but I doubt much more than that. Look at the money we pump into Africa and the developing world; without the right society in place, that money just evaporates into short term fixes along with a lot of corruption and waste (not saying we should stop, but we have to do it better than we are).
Entirely possible, but the fact remains that those three companies are not proof that high tax rates still start big companies. Forget about "why", the simple fact is they were not started in times of high tax rates.