Dreamhost PS High Resource Usage Problem, Is It SCAM?

I upgraded my hosting to DreamHost PS (http://www.dreamhost.com/hosting-vps.html) about 7 days ago, and after 3 days of evaluation i find no interest about it and decided to downgrade. But they rejected my request saying that the resource is too high, then came the long negotiation.
My question now is, would domains parked(not hosted) at dreamhost ate up memory of my PS?
Phase 1: Why didn't anyone warn me before the upgrade?

I wrote:

I found a few unreasonable facts about your statement of rejecting my downgrading request:
1. Dreamhost tempted me to upgrade when I was doing fine with share hosting;

2. Dreamhost didn't warn me with any condition or term of any kind, including downgrading would be rejected if memory reach a certain degree;

3. from the facts stated above, this upgrading thing is a total scam.

##comment: The upgrade took only a click of the button.

And their answer:

I'm sorry to hear you feel this way Ruiz. However, your accounts resource usage is above what will work on shared hosting. If we were to move you back, one of two things would begin to happen:

1 - your domains would affect the stability of the web server, slowing down other customers sites, or taking them down completely

2 - your own sites would begin to fail due to the high resource usage.

As such, we can not move you back until you've brought that usage down. However, I can understand why you would feel the way you do. As such, I'm willing to add a $15/mo subsidy to your PS service. What this means, is that the basic 150MB/MHz you have to pay for will be free, all you will need to pay for would be any resources you allocate beyond the first 150MB. If this is alright, let me know and I'll go ahead and add the subsidy to your account.Phase 2: Why my hosting suddenly ate up so much memory?

I said:

I haven't recieved any email mentioning that my domains are using too much resource BEFORE THE UPGRADE for almost ONE WHOLE YEAR, how come suddenly they are? Is it some kind of malfunction or misconfiguration of your PS that causes the problem? If it is, why should I pay for it?

They answered:

It isn't a "sudden" issue. Your sites have been using whatever resources they need for as long as you've been on the PS. It appears you've had spikes as high as 600MB of memory in your usage, and if you look at your graph over the last month: ...