Any application that depends on unique GuruPlug functionality (BT/Wifi/2 ethernet ports/ESATA/etc.) would fail if the same functionality were not added to the original Plug. However, as tylernt said, binaries should work across both devices since the CPUs are the same. Again, it comes down to which applications you are talking about.
If you mean all apps that COULD be developed for the GuruPlug, the answer is no.
If you mean all apps that don't depend on specific GuruPlug hardware capabilities, the answer is yes.
Does this help?