In Red Hat's case, it's because the Palm Treo works fairly well with Linux. As for Zack...? No clue, except that Zack isn't one to spend money on disposable liabilities.
Unfortunately, Palm has yet to find a US wireless provider to carry the Treo Pro. More unfortunately, it will run Windows, so only Zack is left as a potential customer. Zack is the "Avery Wong" of mobile phones:
Palm has apparently started a new marketing campaign for the Treo Pro: "Early and often, Avery Urlocker. Early and often."