Yes, it does seem like a less obvious choice on reflection. One other factor arguing in favor of the older model (for us) is that we already own one of the original models. My plan was to buy 2GB of RAM for the new iMac, and transfer the 1GB of RAM from the new one into the old iMac, giving me the option of maxing out the RAM in new iMac in the future.
Seems like reason enough to tilt it in favor of the older model. BTW, here is another benchmark test.....this one seems to favor the older model 2.4 over the new entry level whereas the other test seemed to favor the new entry level...... Seems to confirm that the two are essentially equal.
http://www.macworld.com/article/133253/2008/05/imac_benchmarks.html?t=201