The whole point of a HUD is to present information up front so your eyes are out of the cockpit. It also allows you to utilise your peripheral vision which is extremely important. Staring in at dials is not the same.
Whilst the aircraft you mention don't have rear seat HUDs (I will take you at your word) I bet none of the pilots prefer it that way.
Aside from the flight parameters on display there is a multitude of targeting information that really does need to be displayed up front to be effective with modern weapons.
I will admit that there are other methods that can be successfully used instead of a HUD but I would contend that none of them are as effective.
My last point is that yes, HUDs are expensive to maintain, but offset that against the cost of a Typhoon and I'm sure you'll see that it's pretty much irrelevant!
BV
