Most people who post their attach ratios are only going to provide very skewed data that has almost no correlation to what the actual attach rate is for the overall user base.
Most of the people participating in this poll are big supporters of the PS3 platform and will have the collections to show it.
And for those who have owned the console for over 2 years, having a collection of 24 titles would only translate to about 1 title purchased per month, which is pretty reasonable for a regular gamer.
Even so, it still needs to account for cutting out both games that were purchased used. Only the first retail sale counts as a unit sold to the publishers; if a copy is traded/sold 100 times, it still only registers as one unit sold.