at JFK the runway textures looks like a default one.
That's not what appears in your screenshot: they looks as the should, since JFK uses a combination of default base textures + custom markings only.
I own the FS9 version and the runways look different.
This because you might have installed a runway texture enhancement package in FS9, that is not in FSX.
Another question is, the surface textures of the airport are loading very slowly especially at JFK and ORD. It look blurry at far distances, its getting sharper when get closer but loading time of the textures is very slow. Is there a way to improve this and make surface of the airport more sharper?
This of course doesn't have much to do with the scenery, but rather your settings in FSX, and your videocard settings.
What effects textures sharpness in FSX is combination of settings, video card settings and cpu/gpu resources available. Sometimes, by increasing settings, you make the situation worse rather than better, because your system might struggle to display everything at the requested detail level so, it will just display the lowest versions of the texture, because it hasn't enough *time* to display the higher res.
If you are new to FSX, it's probably best to frequent some specific forum, like the one on Avsim, which discuss about tweaks and setting extensively.
First thing you can try, is to set the Anisotropic filtering in FSX and set your videocard control panel option to enable forced Anisotropic filtering at 8x or 16x. And, be sure you have set the Max Texture Slider in FSX all the way to the right.
