Not the same...because you're looking at it as if 258 million is different households. We all know that most of them 360 owners also have a PS3.
Notice the number of Gamecubes compared to Wii. Notice the numbers of PS3/360 compared to PS2/xbox. It isn't so much a "lost market share" but rather a changing of market.
PS2 came out 13 years ago. Many of those gamers have moved on. Hell, there's plenty of launch 360 gamers that have moved on. It's not just a different generation of consoles, but we're going to start seeing a different generation of gamers. We're already seeing a large number of gamers becoming more casual gamers, and many of those PS2 era gamers have long since become parents and possibly moved on to casual games for their families.
You're looking at the above numbers as if they're unique numbers and there has been an increase in gamers, when it could be the opposite. Either way, none of us knows. The same way I can't sit here and say "who" owns these consoles, neither can anyone say that marketshare was lost, which insinuates that PS2 era gamers moved over to 360......we don't know that.