True, but I'll be interested to see if that percentage doesn't creep up if they gain popularity and spend money on R&D to improve their client which currently runs far behind steams.
That does tend to happen when market dominance has been achieved in other sectors. Steam has actually dropped the revenue share for big sellers through which suggests that they don't have market dominance, in terms of big players at least. I think the same will also be true for Epic if it achieves the same market position as Steam has now.
On a side note: I always shudder to think what would of happened if EA had come out with Steam first.