A user who goes by the username "Toppc" on the Coolaler.com forums claims to have gotten an engineering sample of the upcoming Intel Core i7-4960X. As a true tweaker would do, he popped the lid on the chip to see what lies below the IHS, particularly interested, of course, in the method of thermal transfer between the CPU die and the IHS.
So let the good news come; the CPU die appears to be soldered to the IHS, contrary to what Intel has done to the LGA 1155 Ivy-Bridge chips. This is good news for overclockers and enthusiasts alike, simply because soldering the CPU die to the IHS allows for much better heat transfer than if the space were to be filled with thermal grease. This means lower running temperatures and thus room for higher overclocks. With the LGA 1155 Ivy-Bridge chips a handful of users would opt to remove the lid from their chips in order to get around Intel's decision to solder, though obviously at the cost of warranty.
Sadly, the image doesn't clearly show that it is an engineering sample of the i7-4960X, so we'll have to take Toppc's word for it.
Intel's Ivy Bridge-E i7-4960X chip is said to feature a clock speed of 3.6 GHz and pack a total of six cores. It is expected to be released sometime during September 2013.
No other explanation then Intel either was saving money or artificially gimping Haswell/IB or both.
Should be Intel's decision NOT to solder (or Intel's decision to use crappy TIM).
This does mean that Intel has no excuse to not solder normal Ivy Bridges now, though.
Actually, the problem isn't that they used the TIM (although soldering does improve the heat transfer slightly), the real problem is that there is a very tiny gap between the TIM and the IHS causing the heat transfer from TIM to the IHS to end up being radiative instead of conductive (radiative is the worst form of heat transfer). This has been proven a number of times from people that have de-lidded both IB and Haswell CPUs.
De-lid a production chip and get back to me.