Why where the callouts 'PC-50, Preformance nominal, 40 seconds' ect removed?
Because they are useless.
"PC<50" is indicated shortly before SRB separation, since it is the first separation cue.
"Performance nominal" is just informative to the crew.
"40 seconds" is only for people who can't see the watch.
Why were there structural spares for an OV-106?
Because there are none. The structural spares had been used already, they had been created for building Discovery and Atlantis and used already for building Endeavour. There are not enough spares for a second orbiter.
Can a Shuttle TAL at a 51.6 degree inclination to BEN? (b/c during STS-125 I heard
Moron called up, and that was a straight east flight)
No, it is not designated TAL site.
What is the highest inclination a Shuttle can achive from KSC?
62.5°
Would ISS missions be possible out of Vandenberg AFB?
No, Vandenberg is only polar orbit or retrograde.
I read in the book 'Universe in a Mirror: The Story of the Hubble Space Telescope' that there was some small talk about a HST Servicing mission in 2010, 2 years after the planned STS-125 mission but the talk was quickly abandoned, could this have been possible?
Sure, if the shuttle program wouldn't have been ended.
Is there some specific reason that Atlantis has yet to carry an MPLM to ISS? Does Atlantis have some specific reason that could have been easily fixed yet never was, hence forth an MPLM on 135?
Atlantis lacks the hardware modifications for ISS flights, because it had its last periodic maintenance too soon for them. The other orbiters have extra hardware for getting power supplied from the ISS and supply power to the MPLM, while it is in the payload bay.
Why was ISS placed into a 51.6 degree inclination? Shuttles can go to a 62 degree if necessary (STS-36)
because higher inclination means lower payload mass for all launchers. The 51.6° is the standard inclination of Russian space stations, simplifying operations.