I have this doubt. For what I have been reading it seems so, indeed you can counterspell and cast the same turn. So, whoever can counter as an immediate action like the abjurer (counterspell) or the arcanist with the Counterspell exploit is able to do both actions.
I have an example which suits this case perfectly:
In the feat Quicken Spell it is said that, as a swift action, you can cast an extra spell that turn.
According to Pathfinder's rules, swift actions and immediate actions are similar, they both happen too fast and don't disturb your round's main action, the difference being that immediate actions can be done in other player's turns.
That being said, it seems reasonable to me that those special cases of counterspelling could be done without interfering in the character's turn main action (full round or standard) just like Quicken Spell does.
So, can a character which can counter a spell as an immediate action still cast his turn's spell normally?