The original Xbox only sold about 25m units whereas the PS2 sold over 150m - even with a slightly better online infrastructure, Sony were streets ahead of Microsoft and that was off the back of the success of PS1 and an established catalogue with no comparable competition. Although the 360 and PS3 gens were only separated by a few million in favour of Playstation, the PS4 sold twice as many units than the Xbox One with a gulf of over 60m difference. Sony have basically dominated Xbox from day one but now Microsoft are making some strong statements with multi-platform publisher acquisitions and consumer-focused innovations and Sony doesn't seem to have anything you can put your finger on.
Microsoft's recent dominance has already forced Sony to move into PC gaming - something they never wanted to do, and one or two more key acquisitions along with this persistent stock shortage will continue to drive people towards Xbox. If Microsoft landed a deal with Unreal that passed competition laws, Sony would be in a whole world of trouble. They really should have made a move for Square Enix and Konami when they had the chance. I'm not all that impressed with Xbox either so far but the groundwork is being laid for the next 3 years.
I've had every Playstation and Xbox going but this is the first time ever that I've felt concerned about Sony. You can feel the panic with them coming to PC so desperately and apart from a few banked exclusives, they don't ooze much confidence and their store along with online infrastructure is horrendous.