Another thing I'm wondering - do game development suites always use platform specific code, or could the code for the exe's they produce be decompiled and recompiled under another OS?
Unless the suite is specifically designed to work cross-platform, there's nothing you can do to get around its "platform-specificity". Programs compiled for different platforms are generally as different as, say, Spanish vs. Romanian, even for platforms that work on the same processor architecture. This is because (roughly speaking) programs rely on the OS for a lot of essential functionalities, and the way to invoke these OS-provided functions are completely different from OS to OS (not to mention the set of functions themselves are totally different).
Cross-platformness takes real effort to achieve. Basically someone has to provide a sort of common interface/library for the various functionalities normally covered by the OS/platform (files, sounds, graphics, etc.). You program against that interface/library, instead of against a specific OS or platform. Then for each platform/OS the common interface/library supports, there are code specific to that platform/OS, that implements the features in the common interface/library using what functionalities that particular platform/OS provides.
In other words, a cross-platform library or suite or whatever saves you from having to write separate programs for each platform, by having the work done for you--it abstracts out all those functionalities that must be implemented differently in different platforms, provides all the different code for each supported platform, and then slaps a common interface on top of it that your program talks to. The provided platform-specific code translates the functionalities your program requires (expressed as function calls into the common interface) into the functionalities provided by the specific OS/platform.
Using the rough language analogy, the cross-platform interface/library would be a common language like English.
Because providing cross-platform support takes more effort to achieve, it's not surprising that most game development suites would just pick the most "popular" platform, like Windows.