Most companies have a waiting area. In a world of smart phones, its really no big deal. I dont see why people would want someone to sit around in a car like that.
Ive had candidates show up to an hour early. Some people have crazy commutes and need to leave extra early or spend hours in traffic. That would be lame to expect them to wait in the car for an hour.
Sounds like you're a reasonable person and understand mitigating circumstances. I can't say the same for all senior management. Some would be annoyed that they feel put on the spot and others would get a bad vibe from the candidate as if they've got nothing better to do than sit in a waiting room.
Also I think that depends on the size of the company. A lot of companies just have a room they stick you in or a common area where you're in full view of the entire office. I don't think that's a good place to be if you're going in for an interview and you're nervous. Personally I'd rather walk straight in with as little wait as possible.
Generally I'd advise someone avoid doing something that could easily give off a bad impression or annoy the person who's interviewing them.
I got the above advice from my father who was a career diplomat. When he'd go to meet very senior government officials (ambassadors, secretary of state, PMs, etc) he would make absolutely sure never to arrive early.
Its not just me but my company. They tend to treat others like actual people. I really like how far they go in welcoming the candidates who interview. Thats part of what made me want the job - the environment they promote.
Honestly, I wouldnt want to work for a company where they made a big stink about me showing up too early. Mind you, I personally havent done it. But a company that would turn someone down over that, isnt a company Id want to work for. It speaks volumes of their culture.
Also, I dont think Ive ever had an interview where they didnt have some kind of waiting room. And Ive interviewed for many small companies, so maybe thats why I feel that way.