We are not and have not been the stewards of node.js to convert node.js developers into paying Joyent customers; rather, we became the stewards because we employed Ryan Dahl at the time (summer 2010), we were (and are) avid and early users of node.js ourselves, and we saw that node.js needed corporate stewardship. The node.js community has come a long way since then, of course, and earlier this year we announced our intention of moving node.js into a foundation -- which is now well underway.
In terms of how node.js fits into our business, we have always been upfront that we have never monetized node.js directly: to the extent we have monetized it, it has been by offering complementary products like an IaaS platform that was designed to run node.js in production[1] and via support and services[2].
I doubt that npm would be very strategic -- but first you would have to answer the question of whether node.js itself is strategic.
There's certainly an element free publicity among developers. How much is that worth?