It sounds like some clarification is required here.
The Devs have confirmed that there will be two different currencies in the game.
MechCredits(If that's still what they're calling them), which are purchased using $(Euros, or Rubles, or whatever). These will be the 'cash' currency. You buy these, and then use them to pay for premium time or whatever.
C-Bills. You get these for actually playing the game. You play battle, shoot the enemy up, and afterwards, you get C-Bills. Some of those go towards repairing and rearming your Mech.
It's been stated that things like weapons or Mechs can be purchased with either MechCredits or C-Bills. Frankly, I imagine the only things you won't be able to purchase with C-Bills will be premium time, hangar slots for more mechs, and premium mechs with a permanent earnings boost, similar to the Founder's mechs.
I'm almost certain that the "XX$ worth of ingame currency" included with the Founder's packs will be MechCredits.
Why purchase something with MechCredits instead of C-bills? A Mech might cost millions of C-Bills, but only cost a few thousand MechCredits. The point that Devs have made many, many times is that in MWO you will not be paying for power, you will be paying for vanity and convenience. Rather than saving up C-Bills to buy that shiny new Stalker or whatever, you can just whip out the 'ole debit card and have it in minutes. Yes, this will lead to the occasional case of clueless thirteen-year olds buying a shiny new assault mech with mommy's credit card and then promptly failing hard with it, them's the breaks.
Edited by Starne, 10 July 2012 - 09:57 AM.