That's really just because the techniques we use now weren't developed then. I'd bet good money that a port of a modern spell checker would perform beautifully on an old 98 machine.

It's easy to confuse the bad performance of old software with the hardware it's on. But really a lot of the trouble is that the solutions we had to software problems back then are primitive and naive compared to the current state of the art. There's no reason that current software design practices can't massively improve older systems.

Hell, just try installing a modern Linux on an ancient PC, you'll see what I mean. Even considering that the hardware is physically slower, your experience is much, much closer to modern computing than 98 could ever hope to achieve.