Market.apk bundles aren't device specific, so the one you installed was probably just ripped from some different phone/tablet/whatever... no conspiracy theory needed here.
The only hack needed for a decent experience is to either modify your system build.prop to make it look like a device that has real market support, or hack the Market.apk itself to make google's servers think your tablet is some device that it isn't.
If all you did was install the APK by itself, some Archos fan developer must have pre-hacked the market.apk in that way, but doing that is relatively easy and common and doesn't mean Archos had anything to do with it.
The only hack needed for a decent experience is to either modify your system build.prop to make it look like a device that has real market support, or hack the Market.apk itself to make google's servers think your tablet is some device that it isn't.
If all you did was install the APK by itself, some Archos fan developer must have pre-hacked the market.apk in that way, but doing that is relatively easy and common and doesn't mean Archos had anything to do with it.