I think apart from Sharp marketing there is the fact that educating US users is a very tough task and requires big money.
And as long as you hide the fact that the Zaurus uses linux to the users, then the Zaurus has to compete with Microsoft and Palms on the same merits - software avalability, ease of use and plain simple suck factor. I think its the fact the it runs Linux which makes it so attractive - sadly only to us geeks.
The US consumers (and friends I know who qualify as general guys) are generally pretty unaware of technology - they cant differentiate between a IE or Opera, in fact dont even know what Opera is, dont know what a bluetooth technology is really about (except that its some wierd wireless technology), are confused when it comes to difference between GSM, CDMA etc, are totally lost with terms like 1xRTT (i cant blame them there), cant see the use of telnet or FTP or SSH, cant be bothered with a console, let alone a file manager on a PDA. Do they even understand what a USB host is for ?
So there you go, all the plus points of the zaurus are lost on the general users. This is one reason why the Zaurus fails aganst the palms and other devices - no big name attached to them (vis-a-vis the US users) and all the strengths of the Zaurus are lost on them. I guess Sharp cant afford to spend money educating them firstly and then selling them to educated buyers.
They would much ratehr sell to a captive audience - Japanese usres and Corporate enterprise guys.