Are all heatsink push pins. Secondly if yes why, are screws not good enough. Its a simple question and im just curious i would appreciate it if you could answer me.

Not all heatsinks have push pins to mount them on the motherboard. Most of the heavier HSF's use a mounting bracket with a backplate and screws. This is much better because they do not cause your motherboard to bend under the heavy weight and they make it possible to mount the cooler with much more pressure resulting in more metal to metal contact, which results in better heat conductance.
Indeed most coolers have push pins because it's much cheaper and easier for more people to install them. In fact even some of the heaviest coolers on the planet have still push pins like the Scythe Inifinty (It weighs about 1Kg!!!). So if you want to buy a cooler like that, double check if they don't sell an additional mounting bracket with a backplate and mostly they will.
Actually the push pins were designed by Intel and it was only allowed to use them on coolers up to a specific weight (can't remember the exact weight).

Hope this makes some things clear to you

i wanted to know becuase i hate my stock pushpin heatsink and im looking into getting a new one around 30-40 dollars with screws or something else so i can overclock and just have a cooler running CPU

Just wondering if you can modify the push-pin design can be altered to do the design Nils is talking about.

I don't think it is possible to mod a stock Intel cooler with screws, but if you want to OC I would go for another cooler anyway.
There are lots of good coolers around for very interesting prices. I don't know what the price for a Xigmatek HDT-S1283 or a OCZ Vendetta 2 is in your country, but if you look at the benchmarks of these coolers and their prices, I would certainly go for a cooler like that.
However, here a principle I explained in my first post comes into reality. These coolers both have push pins as standard mounting system, but like most branches Xigmatek sells an additional bracket with screws for the HDT-S1283 but it also fits on the OCZ vendetta 2. So if you would buy one of these coolers, do not forget to get that bracket for optimal contact between the HSF and the CPU.