hmm, they lower the voltage and lower the clocks too. check out the spec sheet above these are clocked at 675mhz. Standard 250GTS is 738mhz. The previous MSI N250GTS 1G Frozer V2 is an overclock part (760mhz) and has been around since at least August 2009.
These are the same 55nm G92b part as in the 250GTS and 9800GTX. With the lower voltage these will likely not overclock to the 738mhz of a standard 250GTS. It is an interesting way to respin the G92b part to try to clear stock.
I don't think this is Nvidia so much as MSI doing this. MSI probably bought a lot of G92b parts and are trying to figure out novel ways to package them. It is interesting that last year it was all about "overclock and overvoltage" and now it seems that the buzz is about "underclock, undervoltage, green, quiet". wax and wane.
It's the same crap that all the 'green' NV cards have pulled...lower voltage = lower power draw (duh) but requires lower clock speed. If NV marketers were honest (ha!) these would get a '-' (minus) moniker after their product name.