The only thing seen differently with the Ultimate over the Home Premium edition is one hardware protection feature as well as three others for network application. Then add the $100 more on the retail price.
The differences between the 32 and 64bit versions of Windows can be likened hust as easily to those seen when comparing the old 16bit versions like 3.1 and 95 to 98 and newer. 32bit saw a more stable enviroment for the Windows environment without always being faster. XP Pro 64 saw little or no support there while Vista is just now starting to see driver support for hardwares and new program finally being written.
Following Vista the next version will be the last by Microsoft to see any 32bit editions there. The trend is finally getting underway to see 64bit become the common OS while the market is still 32bit for the present time. Vista has five main editions with some seeing both 32 and 64bit releases. Basic, Business, Home Premium, Ultimate, and Enterprise. No one wants the Basic while Enterprise is corporate intended there. Business and Ultimate see more network support built into those two like XP Pro saw more there over the Home edition.