So should the Advance be counted into the sales of the original Gameboy? Where is the line drawn? 

No the GameBoy Advance is exactly where we draw the line

Your facts are 30% inaccurate sir.

Every game that was marketed as "Gameboy Color" but was on a regular shaped cartridge could be played on the classic Gameboy, that was intentional. There's plenty of those games. Link's Awakening is another, I think there's even a few cases where it's the other way around.

The only difference was that "Color" games never had a standard grey cartridge but were always colored (I think usually they were black). The "Color" games that had a cartridge where the top banner stuck out (thick instead of hollow, like how 3DS cartridges have that hook on it preventing them from being used in DS's) were the ones that weren't compatible with older Gameboy models. These were usually only late Gameboy games. The back of game boxes of games released after the Gameboy Color came out also mentioned which models a game was compatible with.

Those Pokemon games were "Gameboy exclusives", but not exclusive to only the Color model. The correct answer is "No", because the back of the box said so.

It's a similar situation with Xenoblade Chronicles 3D on the New 3DS. So that game is (handheld) exculsive to the New 3DS because it can only be played on that specific model. However the new 3DS is a new model of an already existing platform, not an entirely new platform, so you could say it's exculsive to the 3DS family and still be correct.

The GBC is basically an upgraded Gameboy, although different enough that is has to be distinct but not different enough like the GBA to classify itself as an entirely new platform. At least that's how I think of it anyways, some people may disagree and suggest the GBC is it's own platform different from the Gameboy.

Since Gold and Silver are playable on both the GBC and GB then it can't be an exculsive of either, but it is exculsive to the 8bit Gameboy systems.

Only 30%?? Sweet, thats a new high for me. Im getting beter at this facts thing 

Isn't the Game Boy Colour to Game Boy equivalent to NDSi to the NDS?

It would be weird to categorize it, but I guess in this case, it would not be an 'exclusive'

Never knew about this :O

Does anyone have pics comparing both games/systems?

Gold/Silver on Original Game Boy:

Same game on Game Boy Color: