drebin,
I am not sure - I guess it is possible I was not clear enough in my post - obviously it would be bad if Store does not care if anything else is running on the machine and just takes up RAM as it wants. That's why it said:
1. Exchange Store will grab as much RAM as it can if it thinks it needs it, yes. But - we constantly monitor the performance of the system in regards to memory usage and we can use this data to infer when we need more memory and when other applications or the OS needs more memory.  We then use this data to act accordingly. This scheme allows the system to act as if there is explicit control when in fact it is actually a few autonomous applications cooperating in a disconnected manner.
In other words - we will decrease our (store) memory utilization as needed on the server too. Hope that clears it up?