Unfortunately not all networking kit makes that easy. Here in the UK Virgin Media have started supplying their horribly misnamed SuperHub, which acts as both a cable modem and a router/switch but it only allows MAC reservations within the DHCP lease pool (and if you try to cheat by shrinking the pool once you've defined the reservations, it kindly deletes them all for you). I prefer to set up all devices within my home network with static IPs using MAC reservation and then to prevent the dynamic addresses from accessing the outside world, so this particular piece of junk aggravated me greatly.
It sounds like you're confusing a static address and a
DHCP reservation - they are similar in concept, but different in reality. DHCP reservations will
only work in the presence of the DHCP server on which they were set, static addresses, which have to be set at the device, will work even when there is no DHCP server. Think about it this way - if the address is obtained using
Dynamic Host Control Protocol, then it's a
dynamic address, not static
Whilst I am aware that some devices allow you to set DHCP reservations outside of the lease pool, those devices are the ones that are not working correctly as as no DHCP server should be able to lease an address that's not within the pool, so if what you say, is correct, the Virgin Media SuperHub works properly.
"Shrink" the lease pool, set your DHCP reservations within the lease pool, set your static addresses
at the device, outside of the lease pool, and all will be well