I went to runbot where there's the demo data. I created a new product. It's inventory is zero. It is "make to stock" and to "buy". I ran the scheduler. There was no draft purchase quote generated. What am I missing in this process?

have a look at the procurement exceptions (Warehouse > Schedulers > Procurement exceptions). OpenERP tells you what's wrong with the procurements (e.g: missing supplier on the product form)

It would make sense that the scheduler would balk if there was no supplier in the product. But, there was no such exception generated. In fact no exceptions generated by me in these trials.

if that's true, it could be a bug. but you can also try to run the scheduler more than once, because it has to run N times according to the number of bom levels of the procured products for instance.