The i3 has never been able to overclock (as far as i know) because i3 is a budget cpu for people who can't afford a better processor.
		
		
	 
The first generation i3s (Clarkdale) could be BCLK overclocked, and oh man, could they be overclocked! I've picked up three i3 550s on various Fry's deals (averaging out to about $60 a cpu) and all three run at over 4 GHz without breaking a sweat. No added voltage necessary and only slightly higher than stock temperatures for those overclocks. I ran one of them up to 4.5 for awhile, but it required some extra voltage and since it's just in an HTPC there wasn't much point. 
At any rate, even though the 550s run at higher clocks than my i7 860 and i5 750 can, there's still no comparison between them. The i3s are very capable, but the quads are so much more powerful, smoother, and responsive at all times that there's no contest between them. Likewise, I doubt an i3 2100 or whatever the Ivy equivalent is would be of much interest to those who really can use / need a 3570K or 3770K even if they could be overclocked. If all you do is game, though . . .