==and I doubt that the Jordanians want much of anything to do with the Palestinians nowadays
The vast majority of them live there already--GGG
You're correct in that there is no difference in ethnicity; however, there is a gulf between the two culturally & how they view themselves in nationalistic terms.
One problem with the Palestinians is that they have been used too long as a "wedge" by other Arab & Middle Eastern nations to delegitimize, destabilize, or otherwise destroy Israel. The result is a Palestinian people that is radical, murderous, barbarous, and savage. No sane leader would want them added to his country's population. Unfortunately, none of the Middle Eastern countries or other liberal groups responsible for perpetuating the Palestinian "refugee" population will ever be held accountable for the damage they've done.
In regards to current events, it may be interesting to look at Black September in Jordan in 1970 and the current war between Israel and Hezbollah today. See this link:
http://en.wikipedia.org/wiki/Black_September_in_Jordan
When threatened with a Palestinian militant force that was intent on taking over the country in 1970, Jordan crushed the militants and drove them out. Today, in Lebanon, Hezbollah is essentially running the show in about half the country, and the gov't of Lebanon is either incapable or unwilling to exercise its authority.