We've got a 1998 Mazda MX5, purchased as a used import. I just took a look at the battery that came with the car when we bought it 10 years ago. It looks like it's got a date stamp on one of the terminals "04F", so I guess that could mean 2004. Anyway, the battery is at least 10 years old, it's unlikely it was brand new when we bought the car, so it's probably 14 years old - and it's still going strong. (Not superstitious - but touching wood as I type that anyway).
I'd read that some people had got well over 10 years life on the original Na MX5s, which came out from about 1989, these had Panasonic brand batteries. The battery in our MX5 is a "FB - Furakawa Battery" brand. It looks like a perfectly standard sealed lead-acid battery. Only thing I can think of that's different, is perhaps the battery is larger than you'd expect to find in an 1800cc car these days, but also the battery is in the boot, so there'd be some voltage drop over the long cables to/from the starter and the alternator, but I'm unsure how that could affect battery life.
It leaves me with the nagging thought that the makers can make long-life lead acid batteries, and have known how to do this for decades, but choose to make batteries that don't last very long by design.