[quote:3636e655d8="Team Fail"]...[/quote:3636e655d8]

Suppose you have a ROM and you translate some lines in it from Japanese to English. Then the patch will be something like a list of commands like "At location XYZ, change XXXXXXXX to YYYYYYYY".

And even when ROMs are expanded, the size is usually insignificant compared to the original size (otherwise patching doesn't really make sense)

Now with two differently compiled versions of a game (like in the case of prototypes) almost every piece of data in the ROM is in a different locations. Plus, every address is now different so that has to be patched too. The resulting needed patch (done using the IPS method) size is significant enough to warrant including the ROM itself.