> Why do they still have an extra large Caps Lock key in such a prominent position?

Because sometimes you still do want to insert text with all caps, for example as part of an ID. Also Caps Lock as opposed to Shift Look is quite useful when you want to insert caps and numbers quickly, again as part of IDs.

> What does ScrLk key on my keyboard do?

It switches between the cursor or scroll wheel or the mouse moving the cursor or the viewport/document. It's quite useful. Firefox e.g. implements this functionality under F7.

> Why is there an Ins key when practically every text edit field is in insert mode anyway?

To switch, because sometimes you do want replacement mode. Also it is useful for the Ctrl-/Shift-Ins, which is the original CUA key for what people now know as Ctrl-C/V. It is quite useful for when the latter means something else.

> How often do you actually use the Pause key and what does it do?

It used to still work for a while in Linux, but sadly they removed it. Also it is still useful for the CTRL-ALT SysRQ, Pause sequence to advise the OS, when nothing else works, or you don't want to shutdown properly. Also it feels quite powerful to tell the computer to be off, and it basically immediately being off.