Perfectly reasonable results in 60 years with a high birth rate.
And a low infant mortality rate. And no war. And good living conditions and decent healthcare. But the Palestinians have NONE of these. Remember? They're oppressed.
Secondly, what you term as "perfectly reasonable" would have to assume a population growth of almost 4% per year (worldwide population growth was 2% in the 1960s, has currently slowed to estimates of 1.5% and might reach 1% by 2015). And now it starts to look perfectly unreasonable. Especially if we are to believe these are an oppressed people with all sorts of problems that they face every day outside the norm of the rest of the world.