To my knowledge, all Socket A Athlons are manufactured like what you describe with the CPU core directly underneath a piece of ceramic. They're built this way to get the core as close as possible the the heatsink surface to make the transfer of heat from the core to the heatsink more efficient.
All Athlon heatsinks, regardless of where they came from or who made them, only make contact with that ceramic block. When replacing the stock heatsink with an aftermarket one, you only have to put thermal grease on the CPU core. If you try and put it anywhere else not only will it not make contact with the hsf unless you lather it on really thick but if you're using something like Arctic Silver, which is slightly conductive, then you'll wreak havoc with all those little bridges on the top of the chip.
This is why AMD only recommend you use the phase change pads they put on the bottom of the stock HSFs: If you use something like Arctic Silver and subject the chip to massive swings in temperature, there's a chance the grease can be "pumped out" from under the HSF, possibly shorting out the bridges in the process. According to Arctic Silver, this only happens with temperature regularly gets above 100 degrees C making the chances of this occuring pretty slim for most people - at least according to them. I must say though that I've been using Arctic Silver for a couple of years now on various CPUs and I haven't noticed anything amiss yet.
If you're going to try replacing the HSF then there's one thing you need to know: due to the design of the chip packaging and the way the HSFs mount onto the socket a lot of pressure get exerted onto that piece of ceramic. If you're not careful in fitting the new HSF then it's possible to break the ceramic and effectively destroying your chip. There are a number of ways to avoid this but the simplest and cheapest is just to be careful. Take your time and if it doesn't fit right or you need to put a large amount of pressure on it (it's normal to have to put a bit of pressure on) then stop, take it apart and check you're not doing something stupid like putting the hsf on the wrong way (most have a lip that fits a part of the socket meaning they only go on one way). I've installed/replaced the HSFs on my Athlons here over half a dozen times and haven't broken a core yet.