The NodeID is simply an auto-generated integer on a table. It is not unique per site and does not represent a location in the content tree. The combination of atleast the NodeID, NodeLevel and NodeParentID represent the location in the content tree. The NodeID field resides in the CMS_Tree table. The CMS_Tree table holds all the hierarchical data for the content tree, template ID and structure of the pages on the site.
The PageID is actually the DocumentID field that resides in the CMS_Document table and again, is an auto-generated integer on that table. The CMS_Document table stores the editable text and image data (for those webparts), metadata, style information for the navigation if you choose to enter it, latest version and workflow information, etc.
Only in the event that you create a linked page will the Page ID be the same on both instances. Even if you copy a page to a different location, they will still be different Page ID's
Hope this clarifies things a bit more.