Hummm ... do they believe it?
Well, it is all about embedded notions of the afterlife, I reckon. And a lascivious "earthly pleasures abound" paradise is very much an embedded meme in the Islamic world, particularly when connected to "religious" sacrifice. It is very possibly connected to Islam's heart as a desert religion where an exulted state would mean an existence where things were materially palpable and plentiful; it is food, it is rivers (of wine no joke), it is sex, it is physical pleasure all of which is the opposite of the stripped harshness of the desert environs.
In Christianity, however, the opposite is true. The afterlife is a state of purity, of the soul or mind above the flesh, again particularly when connected to "religious" sacrifice -- "we will see the glory of his face", "we will be in the light" etc. This again is also very possibly connected to Christianity's heart as a reaction to imperial civilisation, an atmosphere of physical plenty; it is a rejection of the environs around them, which just so happened to be food, wine, sex and physical pleasure.
So when you are talking about 72 virgins, you 'aint actually talking about 72 virgins. You are talking about the Muslim paradisaical equivalent of 'bathing in the light of divine grace'.
And these notions are kinda nebulous, though very powerful. The most hardcore Christian is not ever going to actually think that they are going to heaven to spend their days in the equivalent of a UV tanning bed with Jesus's face looming over them. Same goes for the virgins. It's the notion of exceptional reward, rather than the practical reality of the details, that is important.