The implication, of course, is that every single home demolished by Israel is a kind of apartheid against Palestinian Arabs. There is a reason they don't break down the numbers - because the truth will not sound nearly as bad as the scary number "18,000" taken out of context.
So, let's try to provide some context with what little information we can find:
18,000 homes over 40 years comes out to 450 homes a year. So barely more than one house every day over 40 years is being destroyed in the entire country. Hardly what one would expect from systematic ethnic cleansing.
In 2005, Israel destroyed 1200 Jewish homes in Gaza alone, and I don't know how many were demolished in "illegal" settlements in the past few years but it is probably in the hundreds. Israel also destroys illegal Jewish homes within the Green Line and destroys illegal extensions on Jewish homes in Jerusalem. So for this decade, it appears that Israel has destroyed about as many Jewish homes as Arab homes.
According to the EPA, over 300,000 homes are destroyed every year in the US, mostly in inner cities. Assuming that the US is about 50 times bigger than Israel, this means that the US destroys about 13 times as many homes per capita as Israel every year.
In addition, Palestinian Arabs are building illegal homes much, much faster than Israel is destroying them. 6000 illegal Arab homes were built between 2001-2005, far dwarfing the numbers demolished by Israel for not having building permits.
But advocates for Palestinian Arabs at the expense of Palestinian Jews do not have the intellectual honesty to give any information out that might weaken their cases.