Not so unusual...
Although this might be a first of Intel on the desktop, the Xeon line has for a long time had low-power versions of chips which are slower than cheaper chips but have the benefit of lower power requiremenets, for those whose priority is either noise (workstations), lack of cooling (blades) or power bills (especially in co-location hosted environments).
I have for the last few years used these chips as they are fast enough for the jobs we need them to do, but allow us to fit more servers in an expensive-to-host rack without going over the power budget.
For a basic example, see for instance the L5420 ($380 list) versus the E5420 ($316 list) - same speed, # of cores, FSB, cache, but burns 50W versus 80W.
I haven't any experience of them, but my understanding is that AMD's Athlons have low-power versions on the desktop.