I haven't seen any firm evidence of either's launch date other than Sony putting up "Holiday 2013" at PS4 conference which could mean any Fall month.

What!?  I haven't heard a single rumor to that effect and wouldn't that cut their sales in half?  Hell San Andreas sold more on PS2 alone than GTA4 did multiplat so I highly doubt that.

Well, didn't Xbox exclusivity for Liberty City Stories cut their sales in half?

Yes, of course it did. But you can bet that Microsoft made it worth their while.

That was timed exclusivity.  I got the complete edition for PS3 last year with both DLCs in it.

September is not a holiday month. Holiday means Nov-De c. Be realistic here.

I don't know.  I see holiday programs starting in September.  I would definitely consider late October holidays and that could work too.

It needs to be out before all these blockbuster titles around the holidays.  COD, AC, BF, and many more will come out in October/November and PS360 will most likely have them too.  It could help out significantly with software sales of the new console and hardware sales if it can be out before these games release because people aren't gonna wait for them.  Look at how WiiU got almost no sales of AC and COD this past year.  Sure the crowd is different, but the fans of those games also had already bought them for other systems.  Watch Dogs could end up being like that if it comes out in October and PS4 isn't here till November.  Worse if Nextbox launches first it will become the platform that everyone's friends have these games on so they will lean more towards getting that.  This is a big deal I think and it would serve them well to get out ahead of the holiday titles flurry.

How important is this aspect do you guys think?

I dont think it matters that much really, because most of those AAA games will be also available for the PS4.   Battlefield 4 will defenitely come to the PS4.   And even If Sony moves the cards right, they might even get GTAV for the PS4 too.  Yeah, they would come later, but a lot better.  That is why I think they are launching in November, so Rockstars can have some month in order to make the PS4 version available.   But that is not the main thing about the PS4, what Sony wants is that people buy a PS4 not for a better version of AC or COD, (like Nintendo wanted when they released their console) but for Killzone, Infamous, Drive Club etc.   Those launch games are AAA quality and will sell like crazy. Meanwhile the better version of current gen games will sell nicely, not as much as current gen, but still they will sell good, because you will be able to play them with steady frame-rate, better resolution, and more improvements.

The WiiU versions of AC or COD games had almost no sales, because they did not bring something new to the table, and the console was not all that next gen to begin with, so most gamers did not give a damn.   I think it will be quite different with the PS4, because of what I explained earlier.  The first PS4 adopters will be PS3 users that want to play another Killzone, another Infamous, another quality AAA racing game.   They cant make people buy their console because of COD, because you can still have the core experience on the PS3, so why would you buy a new console for it, whether it comes in september or november. The point of enhaced ports is so that those bought the console early, can get them enhanced.

For me personally, that I will buy a PS4 day 1, The only PS3 games worth buying till the PS4 comes are: GOW:A, TLoU, Beyond, Bioshock:Infinte and C:LoS2.  If they have a digital version even better, because that way I could eventually play them on the PS4.  I say this because it is much guaranteed that most AAA current gen games will be also available for the PS4, but those are not the main reason I want to buy a PS4 for.

Also, I really dont think M$ will launch earlier, at most they will arrive at the same time.  But I still think the PS4 will arrive earlier, because when M$ announces their console, they will want to overshadow the PS4 announcement so they will have to realse more info, including price and date; and because of that Sony will pick an earlier date to screw them over.  Sony this the february event because they are ready to deliver the console, while M$ is not.