I'm not so sure they ever will pass the XBox 360 ...
In the near future the PS3 will be lucky to outsell the XBox 360 on a worldwide scale by 75,000 to 125,000 units per month; this would essentially have the PS3 matching the XBox 360 sales outside of Japan and their Japaneese sales would be what was letting them cut into Microsoft's lead. At that rate it would take Sony 4 to 7 years to catch Microsoft. The problem is that this is not a likely scenerio ...
What I think the most likely scenerio is that Microsoft's crushing lead in North America and moderate lead in the Other's region will force most western third party developers to produce an XBox 360 version of any PC or PS3 games that they make. At the same time as this is happening the Wii will be attracting the bulk of Japaneese (and worldwide focused) developers whilst western third parties still focus a lot of attention to the Wii. The end result of this developer distribution is that Nintendo (by default) will get a lot of exclusive titles, Microsoft will be able to pay a little money to secure exclusives and Sony will have to pay money to secure ports of games.
Ultimately, the XBox 360 will have more games, more exclusive games, and often the higher quality version of a game while being sold at a lower price which means the PS3 will never be able to match its sales outside of Japan. Even with their sales in Japan the PS3 will have a great deal of difficulty outselling the XBox 360 by more than 25,000 units per month regularly which means that it will never outsell the XBox 360.