The Android Marketplace is currently restricted to "Smartphones" only. Hence the reason it's unavailable on the Archos tablet.
A 'persistent data connection' is a stipulation from Google for Marketplace certification. Something not really available on wifi only device, which is what some consumers obviously want in a tablet.
So even though the Samsung Galaxy Tab has Marketplace access, you cannot purchase apps in in the majority of countries, and developers are unable to sell apps in the majority of countries.
If Samsung want to beat the iPad (and obviously they do), that's an issue that needs resolving right ?