Gamers, especially Xbox owners, love Phil Spencer's statements about cross play. You might think Phil magically dropped from the sky to save Microsoft in their darkest hour and free gamers from the oppression of the cold, money driven game industry. Get real folks. Phil has been a Microsoft employee for 28 years. As the head of the Xbox division, it is his job to increase Microsoft's market share.
There are no coincidences in the gaming industry. When the Xbox 360 was in the lead, Microsoft [i]never [/i]mentioned cross play. They loved buying up exclusives and required an Xbox Live Gold subscription to use the interenet. Before the visceral reaction to E3 2013, they planned on selling an Xbox One with digital only games and a 24-hour check in. How many tweets did Phil Spencer send decrying these practices? Zero. Only after the PS4 was selling almost 3:1 against the Xbox One did Microsoft start making moves that players like. They dropped the Xbox Live Gold requirement to use the internet, began working on backwards compatibility, dropped the Kinect 2.0, and dropped the price of the Xbox One to compete against the PS4. The price drop was the biggest driver of sales, and now the PS4's sales advantage has narrowed to 2:1, with the Xbox able to beat the PS4 in North America for a couple of months.
Phil's talk of cross play is all meant to drive Xbox sales. The 2:1 lead means that if gamers go where their friends go, they will buy a PS4. Cross play removes that incentive to go PS4. However, if the Xbox ever overtakes the PS4, cross play would work against the Xbox. How much would you bet that if Microsoft ever rises back to the top of the console market, they would turn off cross play and give some bs excuse like "preserving player experience with our superior network". You might say Microsoft already promotes cross play with PCs, but I respond that they limit cross play with their own Microsoft platform and not services like Steam. Xbox hardware may be a break even business or maybe even a loss, but the Windows business is pure profit. It doesn't really matter, though, because Phil never expected Sony to change the status quo and allow cross play with Xbox. His goal was to make Microsoft look good and Sony look bad. Gamers and the gaming press took the bait.
tl;dr Microsoft is still Microsoft.
[spoiler]I say Microsoft was in the lead with the Xbox 360 and that is only true for early days of last gen. The PS3 eventually caught up to the Xbox 360, with about 80M consoles sold each. Both trailed the Nintendo Wii. The Xbox 360 was considered the dominant force last gen because it had the highest attachment rate (games sold per console).[/spoiler]