Sometimes, the cost of memory is very prohibitive, particularly if you're talking about makers like Crucial.
And that's not to imply that Crucial memory isn't good, though what I am saying is that do you really need the most expensive memory you can find, especially since OWC memory is as good (my computer works just fine) and its not only cheaper, but comes with a LIFETIME guarantee!
In fact, why would you use anyone else's?