Bar Code wrote

http://www.spaceref.com/news/viewsr.html?pid=9926 talks all about
electric ion engines but doesn't mention nerva type engines. Why?

He's concerned with very high Isp engines; Nerva-style nuclear thermal
rockets have Isps only modestly higher than chemical ones. (Note
that in the rocket equation, "modestly higher" can make a substantial
difference in system performance for some applications.)