This ignores the basic economic reality of “marginal value”.
Think of it in terms of pork chop sandwiches. You are offered 72 pork chop sandwiches to eat for lunch, as reward for shoveling out the contents of a cesspit. Seeing you slacking off after a few hours of shoveling, they offer to sweeten the deal with four more porkchop sandwiches, if you pick up the pace and get that cesspit emptied.
You are hungry, so look forward to the first four sandwiches, but after that you realize it will get harder and harder to eat the other 68. But you manage to slowly pack them away during lunch, after which you are bloated.
So what is the value to you of a bonus of four more pork chop sandwiches?
Law of diminishing marginal utility.
File under, ‘They think of everything. ‘ Please note the final line:
‘Also reported in Sunan al-Kubra and Musnad Ahmad ibn Hanbal, and declared sahih (authentic)[9] by Ibn Abi Shayba, Ibn Hibban, and al-Hakim is the hadith that states the servant in Paradise will be married with seventy wives and that they’ll be given the sexual strength for a hundred.’[37]
http://wikiislam.net/wiki/72_Virgins