Since you've not used any processor specific switch such as -xHOST the only other possibility one can think of is that the versions of GCC on the different systems could be different. Since iCC is GNU based and relies on the GNU distro (uses its asm, ln etc) the compiler doesn't include replacements for std C++ headers (except for some very specific scenarios) and will use whatever comes on the system. And, if they are different the code generated by the compiler can be different as well and hence the code size can be different accordingly.
Other than the above reasoning, the only other difference you may see is the timestamp/date and file paths included in the binaries and that again shouldn't be too significant of a difference thereof. Hope that helps.