Google in the US does this. I was on call for my team about once a month and at the end of the year, the bonus for merely being available was quite large. (I think it was something like $1600 a week, but I could be misremembering.)

My understanding is at Google it's counted as 33.3% time for every hour you are on-call with a 30 minute response time.

And 66.6% time for every hour you are on-call with a 5 minute response time.

I believe that is for SRE teams. SRE teams are much more reasonable about on-call, having enough staff to have the on-call person on-call during their workday, not at 3am their time.

SWE teams often don't have the global coverage that entails, so they just pay you extra to be close to your phone.

Yes, Netherland. It's entirely possible it's required by law to pay people for the time they work, so that could explain the difference.