98% of the ISP's I've worked with use OSPF and BGP.
The bare-bones implementation of IS-IS is a drawback for
these "serious", but smaller, ISPs.
Plus ospf, if configured properly(address summarization, redistribution) is easier to configure and manage.
If you have hardware that won't handle ospf when configured properly it won't handle IS-IS either.
In short, I disagree.