Giovanni Drogo in
engr.vans.vg:

(Hatunen
I see at http://bahn.hafas.de that there is only one direct train from
Munich to Koblenz and it's an overnighter, so it looks like you're
going to have to change trains at Cologne.

Seems a strange way ... it will mean going back from Cologne to Koblenz.

That was my thought, too.

I see lot of IC trains doing Munich to Koblenz with one change either
in Frankfurt, Stuttgart or Mannheim.

That sounds reasonable, without knowing the details of the courses.

I do not know the recent patterns of service for ICs, but in
pre-unification Germany
correct description snipped

A change in that area comes from the high-speed route between Frankfurt and
Cologne, making this stretch (close to the A3 Autobahn) remarkably faster
(by at least one hour) than the traditional Rhine route via Mainz and
Koblenz. I imagine that Hatunens observation comes from this issue.

OTOH, I thought of the Thalys from Cologne to Paris, though there is a
connection Koblenz - Saarbrücken / Luxembourg - Paris, too.

However, Spencer will have a reason for his choice, whatever it is ;-

Ciao,

Paul