Some others here are comparing to Windows but the parent commenter here was saying it was a shift for Apple, so here's a snapshot of that from a machine I used

Some others here are comparing to Windows but the parent commenter here was saying it was a shift for Apple, so here's a snapshot of that from a machine I used to own: 10.3 Panther required a G3 or better and USB, which (in laptop-land) dropped the pre-Lombard G3 Powerbooks from 1998. So the 2003 OS dropped 1998 machines, so just 4 years of coverage. "Security vulnerabilities" weren't exactly the same thing in those days as they are today, with less online apps, but in a way it was also more obsolete more quickly because hardware moved quickly: you could have a 233Mhz to 300Mhz 1998 G3, but the new 2003 Powerbook G4s were clocked at 867Mhz-1.25Ghz - nearly 4x across the board. I get more usage out of 5+ year old Macs now than I ever did in the past.