It's very impractical/expensive for mass products to make the surfaces in question so flat that no thermal paste would be needed. Many tests and reviews have been done. Even if top-of-the-line coolers came with perfectly flat surfaces, Intel's heatspreader is not -- otherwise it would cost so much more. Also, heatsinks can be applied with a lot of force, which usually pushes out the "unneeded" part of the thermal paste. In a bind, even lipstick, toothpaste, chocolate and other silly compounds work better than nothing, so I'm not surprised that you're getting ok results even with a touch of thermal paste.

A fun thing to try is using a modern low-end CPU (latest i3s, Pentiums, Celerons) without its cooler. Not advised by Intel, of course, but you might get into your OS of choice even before it starts throttling. I'm somewhat comforted by the fact that a CPU automatically powers of once it reaches something above 100 C (103 maybe?) and throttles a few degrees before that. Those temperatures shouldn't leave the silicon damaged.

In practice, thermal paste is a must. If you don't like those (I personally don't, they get everywhere by accident and can be tough to remove), try getting an IC Graphite Thermal Pad which is reusable and rivals really good, if not the best thermals pastes, according to the limited number of reviews I've seen. I think that its practicality beats better results in non-highest-end applications.