There's a superb column by Barry Rubin in today's Jerusalem Post, which introduces a reality check into some of the praise heaped on Salam Fayyad after his speech at the Herzliya conference (which I was at). Do read the whole thing, but his key point is that whilst the fact of his presence, and his tone, might have been conciliatory, the content was anything but. 

Fayyad demanded that Israel must unilaterally pull out of the rest of the West Bank, getting nothing in return; it must immediately stop all construction on settlements; the IDF should never enter PA-ruled areas, even if the PA doesn’t arrest terrorists who have murdered Israelis or are planning attacks;
Israel should end its blockade of the Gaza Strip, even though the Hamas
rulers there refuse to make a deal with the PA, openly announce their
goal of destroying Israel and smuggle in as many weapons as possible.

As Rubin puts it:

Fayyad
is the most moderate guy in the PA leadership. He was doing about the
best he could. But that’s the point. He has no base of support, isn’t a
Fatah member, and doesn’t really represent Palestinian thinking. He is
in office only to keep Western donors happy. Thus, Fayyad couldn’t go
any further because he knows his Fatah bosses, Palestinian constituents
and Hamas enemies would throw him out if he offered the slightest
concession and demanded any less than everything they want.

...Since 1993 not a single
Palestinian leader has ever made a speech to his own people like
Barak’s, never said that they should have to give up something to get a
state other than their claim to all of Israel (which they don’t quite
seem to give up), never urged the media and public debate to become
more moderate.

Here's my explanation: they don't actually want talks.