My Reeboks always held up better than my Nikes, actually. I've had cheaper shoes that are better than both, like my current waterproof Faded Glorys and Globes.

I don't know for sure but it could have been that Reebok was already an official sponsor for the Ironman competitiion along with Isuzu so they went with them on that basis.

Remember the old pump-up Reeboks? I liked SNL's spoof on it with the pump-up Thanksgiving turkey, if you've ever seen that. :-)