Pci Compliance Question Attn: X-Cart And Cs-Cart

have a question about PCI standards.

In my evaluating different shopping cart systems I looked at CS-Cart X-cart and a few others.

I thought I had decided on CS-Cart due to the fact that they are promoting PCI Compliance. However today I was doing some more research and I noticed on X-Carts FAQ page they talk about how the shopping cart program doesn’t need to be PCI compliant, only the Merchant account.
Can someone please explain this to me?

X-Cart: so if I have a customer who checks out and I am using the X-Cart system is the customer taken to another site where they can enter their CC info? Sorry, I wanted to ask this question on your companies Forums but they are locked down for customers only for some reason. Also, I notice you have Innovativegateway but no quickbooks merchant services? Both are Intuit software, why no support for both?

So my other question is: What does CS-Cart do different that allows them to claim PCI compliance in their marketing pages.

This is important because it will really affect my descission on what cart software I may go with.