The American system isn't without its eccentricities, but that's true for every country, I suppose.
> in most countries the legality of abortion would be decided by elected legislators, rather than judges who are appointed for life
State legislatures are doing that job. That there is no federal law on the issue of abortion reflects both that there is no unanimous consensus on the part of the people, as well as some level of craven political maneuvering (since abortion has been a big draw of people to the polls). At various times in the past 10 years alone, there were periods where both the Republican Party and the Democratic Party had control over the presidency and both chambers of Congress. A federal law of some kind, in either direction, could have been passed at those times (though perhaps subject to constitutional challenge).
High-level judges appointed for "life" (and by this I include age-capped retirement) are not unusual in developed countries. The German Bundesgerichtshof, the Australian High Court, and the Supreme Court of Canada all have this. The point, of course, is to promote the independence of the judiciary from the other parts of government.
> in the US the government can just 'shut down' for some reason, and this is just a normal sorta thing
The power of the purse is in the hands of the legislature. When an annual budget fails to be passed, the executive no longer has authority to spend money, and kind of goes on hibernation until a budget is passed.
Parliamentary systems have a different kind of shutdown, where if no ruling majority forms, then a caretaker government comes in with no mandate from the people to substantially change any policy. This can last much longer than any US government shutdown; Belgium had no leadership in parliament from 2007 to 2011, for example.
> It's far from obvious how these eccentric features could have influenced the founding of the likes of microsoft, intel, apple, facebook, google etc.
Well, sure. You pointed out various frivolous (to economic behavior, at any rate) factors that have nothing to do with entrepreneurship or laissez-faire capitalism. It would be far from obvious to anyone how abortion policy relates to the founding of companies.