I recently saw a YouTube video of an Intel rep stating that all of the chips since Sandy Bridge, including Ivy Bridge and Haswell, are 95W "Power Envelope" chips, and that although the TDP has changed between the high-end versions of these chips, the 95W figure has been part of each chip's design. This statement makes a lot of sense when we take into consideration that initial Core i7-3770K chips sold were marked as "95W" until people's complaints had Intel change the packaging to say "77W". It might also change how you look at these Haswell chips since both Ivy Bridge and Haswell are 95W "Power Envelope" designs on the same process but Haswell has way more functionality on a physically larger die, so its higher cooling requirement only makes sense. As simple as that sounds, it might not exactly be that simple because unlike older chips, the larger Haswell die is also offset from the center a bit, which makes the cooler's orientation even more important.
The design changes are pretty obvious on even a physical level once you remove the IHS on a Haswell chip. Once mounted into the socket, the CPU die sits parallel to the DIMM slots in most motherboards, so coolers with heatpipes might work best with the heatpipes lining up horizontally, not vertically (as you can see in my mock-up picture above). Our cooler reviewer, Crazyeyesreaper, is investigating this matter with his own Haswell test rig, so expect to hear him report about his findings in regards to this query soon. That said, the better performing of a cooler you can get for your Haswell CPU, the further you are able to push your chip. A fully customized water-cooling loop would be my personal recommendation for a decent long-term overclock.
One added consideration with the Haswell platform is VRM cooling, especially on mid-grade enthusiast boards and those products falling into the sub-$150 market. These boards often have their number of VRM input phases reduced, increasing the current each phase must handle, which increases temperatures. Heat is a major reason many high-end boards have seemingly overbuilt VRM sections—it's not about providing ALL that power but having each individual component operating as efficiently and with as little heat as possible, which makes sure no heat passes on to the CPU package by way of the board's PCB and CPU socket. Having so many different Z87-based motherboards here, from entry-level to the extreme high-end, I can tell you that a lot of different products share commonalities, but it's always easy to recognize the board's intended use by looking at the VRM section and its cooling. Boards with an "OC" focus usually have pretty basic cooling since liquid nitrogen vapors really take care of nearly all the heat. Other boards meant to push high clocks over the long-term have water-cooling integrated into their VRM-cooling solution instead. Those regular $200-or-so boards with relatively basic cooling...well, they might not overclock so well over the long term, and that's perhaps part of the upset we've seen in the past weeks from those that have bought into Haswell early. That's not true in all situations, but I'm confident that many of the issues people have with Haswell are directly related to the additional overall cooling required. That said, a lot of it is still just up to plain old Lady Luck and what you win in the silicon lottery.