I think one of the main issues of the Xbox 360 falling behind in sales has been the dogma that they tend to die a lot.
It still is a major issue, however it is quite confusing that they've now reached the 1million mark here in only a few short months.
As on release they did extremely poorly. Even now it is very easy to obtain a PS3, which are still not selling very well even in the area I live which is one of the richest in England.
While the Wii, DS and Xbox 360 are more difficult. Infact over Christmas here it was impossible to get any of the consoles except for the PS3 and Xbox 360 Arcade. I have a feeling that much of those 1million numbers has been caused primarily by the price-drop and the fact of companies trying to shift their ex-stock (i.e. units Sony have stopped producing like the 60GB and 80GB versions)
Leaving the Wii out of it, the Xbox over Christmas had some phenominal sales. As in November it had sold 12million units (shipped 15million), by the end of January it was up to 16million units sold (18million shipped)
No idea about the PS3, but with them now retiring the 80GB officially; leaving only a 40GB for the time being and no stable news on what will replace it (i.e. larger HDD of 120/160GB is the current theory) it's difficult to say how the public will react.
Although it certainly is only selling faster than the PS2 within Europe. Worldwide it is far far behind. As the PS2 sold 10million units within 12months of worldwide release, it was the benchmark that Microsoft shot for and were only just shy of. (about 500,000 units shy iirc)
The Wii however just totally blitz the record by doing it in less than 4months. It's quite obvious that the Wii is going to be the most popular console this generation, simply because it appeals to a much wider demographic.
As far as the PS3-360 sales go though, I firmly believe the 360 will remain ahead sales wise. Remember the first 12months are always the best (especially christmas periods) for console sales.
While it can be said "But the PS3 has a few huge titles due out" these titles everyone are waiting for will either be available on the Xbox 360 at the same time, or are due out for this Christmas. (MGS4 for example)
When you compare this to the Xbox 360 line-up for this year, which includes Mass Effect 2, Perfect Dark 3, Gears of War 2, Lost Oddessy (Xbox 360s own Final Fantasy from the same creators); plus whatever is officially unvieled at E3/GDC this year.
This year will definately be domination by titles, and with such strong sequals coming to the Xbox 360; along with the new HDMI consoles being able to shake off that unreliability of the console hardware.
That's really what most of the lack of sales for the 360 come down to right now really. I mean there is very little doubt, which is really a better multimedia platform; but people have shyed from it simply because they hear the 360 dies alot.
Something that actually only a very small percentage of them have.
The 360 support dept takes a while to get 360s back to people quite often and it is believed this is because they've got too many cases which is true, but something many should take note of; their support/warrenty dept was setup of the intention of about 10-20 cases a week of hardware failiar. Not 50-60 cases, which has been the problem.
I mean bare in mind that the original Xbox the biggest issues was the power-cord might catch fire, on rare occassions the consoles would die. They thought it would be the same for the 360. Mis-judgement on their part really, but the new machines really do solve this.
Once the stigma of consoles dying is out the door, I really see the 360 becoming a much stronger presence on the market.