Does radio station reception with car radios really vary depending on radio brand or car? It certainly seems to with cars I´ve recently owned. What´s behind the apparently significant variation in signal reception with car and truck radios?

As with any audio equipment, the better the components, the better the signal reception and the better the sound.
Higher end vehicles tend to have higher end audio components already installed from the factory. Some have Bose systems, other may have JBL or Blaupunkt.
That often means you get what you pay for. Many options are available from the aftermarket as well.

Yes! Signal strength is one area. When the radio can pull in a decent signal. Selectivity or how selective the radio is. Alternate channel selectivity or how good it rejects close stations. 101.1 vs 101.3 or 99.9.

Diversity reception for FM makes the fade stop. Separation between L&R channels. Dealer doesn't offer these numbers. Aftermarket does.

I have a home stereo in which the FM only tuner costs $470 in the mid 70's. I can receive 3 stations clear by rotating the antenna. You can also buy a $10 radio today. Yep, there is a difference. Put that $470 in today's dollars.

Then there is sound quality.