a european prosumer device won't work on a US BES for the same reason a US Prosumer device won't work on a US BES, because it's a prosumer device.
The Prosumer or Enterprise status of a device is set at the network, not on the device itself. There are no functional differences between the handset software. Otherwise I wouldn't be able to log onto the Blackberry Infrastructure everyday and change prosumer devices to enterprise and vice versa with a click of a button. If it was built into the OS they would have to return the device to us while we reflash it everytime.