Well it is not Command-R (That would be the CMD key "Plus/Also" (and I'm not sure why you are typing the Minus sign) the Shift key and the r key "R"). It is the Command key "Plus/Also" the r key (No Caps) held down together just after the startup Chime sounds.
If an Intel CPU base Mac can run Lion, is capable of running lion (Some can and some can't), it can start from the always included Recovery HD partition by using that key combo.
Now there are some Mac's that will not start from that key combo but it has nothing to do with the base computer, model year of the Mac. It is because that Mac is using FileVault encryption. Because of FileVault that key combo is disabled. Otherwise you could boot to the Recovery HD partition and Erase the Encrypted partition.