Yes, it is. This is mainly because of the way Blackberry was initially designed: some of the Blackberry apps simply do not work without a SIM card. So we were forced to have the so-called BES5 –capable SIM cards; which are SIM cards for Blackberry handsets.
Secure Phone, on the other hand, does not suffer from that inherent restriction. This is why Secure Phone users may actually never use a SIM card; whereas Secure Blackberry users will always have to use it.