1-The gap is still growing in ps4 favour
2-One game is not enough to change anything,sony had big ip too sure not as big as Halo but it still help a lot+3rd party games will help ps4 more then x1
3-Like you said they could buy a ps4 or an x1 but they will probably choose a ps4
4- With no 1 year start the cost of production of ps4 could fall as fast as x1 so ps4 could get a price cut too rapidly after x1
5-Not true American buy the console they think is better to prove that ps2 destroy xbox in usa and sold even more then xbox360
6-Sony said they could produce 1 millions a month with summer consoles don't sell a lot so they can prepare a lot of stock for holiday
7-Nobody will buy a console for multimedia functionality if it didn't help x1 now why would it help it in future
8-Some people say the opposite so it depends of taste
9- x360 buyers choose ps4 instead of x1
10-Microsoft can buy only medium IP it won't change the situation a lot but big IP will never go exclusive to any consoles and those big IP are the only thing to make a difference.