This is correct. After the events depicted in Halo 3, the Flood outbreak has been quelled and the Gravemind destroyed, but samples still exists with the Forerunner facilities.
The difference between this event and the last is that those who eradicated the Flood remain behind to deal with the remains of the infestation. The Flood are no longer a mystery, nor will the Forerunner technology (most importantly the array) be seen as spiritual artifacts to be claimed and used for some divine purpose.
True, but now that we have the knowledge of the Flood's storage(obviously, as there was a Gravemind on Halo Delta and an unknown populous on Halo Alpha) on the Installations, I think it's somewhat safe to assume that the Elites and possibly mankind(if we by some odd chance manage to receive Elite tech, possibly by a treaty, we could rebuild a fleet) would hunt down the installations near our part of the Galaxy, and glass them or otherwise destroy them.