It kinda prevents the abuse, yes... I just prefered it like this, as it would increase the useflness of the spell in a non-muchkin fashion. This would allow you to re-shuffle a spell book given to you/ bought by you/ Found as loot.
Normally, the above circumstances would always require you to need a spellcraft check to prepare the spells as the book wasn't penned by you, even if you owned the book for years and years.
IF you feel that you don't want the spell to be used in the above fashion... then revert back to the "must not have to make a spellcraft check to memorize the spell" version, just remove the " must be known by the wizard " part.... else it could get confusing...