Maybe some computers come with Office as a promotional deal, and if they do, that's up to the OEM, not Microsoft. Nonetheless, I've not seen any PC come with more than a 30 day trial of Office.
See my edit above. With 2010 Office Starter 2010 is an option for the OEM. It replaces Works and the Word viewer and gives a better upgrade path to "real" Office.
http://www.microsoft.com/oem/en/products/office/pages/office_2010_starter.aspx
Office Starter 2010 is not a trial–it has a perpetual license that does not expire. Office Starter 2010 is an advertising-supported base productivity suite that is available only on new PCs. It must be preloaded on new PCs at the point of manufacture. Office Starter 2010 is not available for existing PCs at any time after manufacture; for example, Office Starter 2010 cannot be installed on new PCs being sold by resellers, even brand-new PCs. It will not be sold through distribution or available to end users as a standalone product.
B