Cycling in Melbourne Australia
If it has developed cracks, do you really want to replace it with the same thing? It hasn't 'somehow' got the cracks around the nipples, it is a result of - overloading, ie you are too heavy for the number of spokes; - loose spokes, ie too much movement (not necessarily visible to you) which increases the wear on the rim; - Spokes too tight, ie they have been overtightened and are puling out of the rim, or the alloy of the rime has fatigued ie you've worn the wheel out.
Possibly a combination of all, which makes me think you are better off with a a higher spoke count (remember your rear wheel will wear faster as it has to take all of the drive forces, so the stronger the better). If you are after lighter weight wheels, you will always find a reduced life. Good luck finding what you are after.
John, I would have to agree, the over loading wold be the issue.