You'd have to ask Chris Prillo and Steve Bass why they use it, but my take would be it offers Internet Explorer's compatibility (some websites are still Internet Explorer-only) but also gives the user the ability to use the Gecko engine while adding features possessed by Firefox and Opera. I still prefer Firefox or Opera, but for those who want/need Internet Explorer, but with greater functionality, it's a nice half-way point.
Chris Prillo and Steve Bass of Pcworld use maxthon. It is slow but why do they like this browser? It is even using the trident engine which is very slow.