From the source:
However, Intel plans to release a firmware update that limits processor core overclocking only to Intel Z87 based platforms.
http://www.bit-tech.net/news/hardware/2013/07/25/intel-overclocking-block/1
Intel has long tolerated overclocking on its products, competing enthusiastically with rival AMD to encourage overclocking competitions that allow its chips to hit ever-higher clockspeeds in the name of headlines. The company balances this, however, with a desire not to harm its revenue stream: if customers can get the same performance as a £150 processor from a £100 processor, there's little incentive to spend that extra £50 on a higher-margin product.
Recently, however, several motherboard manufacturers have been releasing BIOS updates for their non-Z-series motherboards - which sell for less than their high-end Z-series equivalents, even when offering much the same feature set - which allow the user to play with the overclocking features of K-series chips. While they don't offer the same overclocking potential as the premium Z-series motherboards, largely thanks to corners cut in other areas such as voltage regulation, they do offer the chance for buyers on a budget to eke a little more power out of their purchases.
However, Intel plans to release a firmware update that limits processor core overclocking only to Intel Z87 based platforms.
http://www.bit-tech.net/news/hardware/2013/07/25/intel-overclocking-block/1