Except I am not sure how much movie playback has ever really mattered in consoles.
I mean, is Blu-Ray playback a big factor in why people purchase PS3's now? How about in the future?
First we have to assume the purchaser is interested in playing movies on the machine. It seems Blu Ray in PS3 has a very low takeup rate in that respect. According to one survey I've read just 22% of PS3 owners use it for movies. To me, looking at the sales of stand alone HDDVD players, then PS3 sales, then actual movie sales on each format, it's stunning to me that Blu-Ray is not dominating much more than it is. I mean, since launch in the USA PS3 has sold 1.1 million consoles in four months. I dont know stand alone HDDVD sales, but <20,000 a month seems to be a reasonable guess. So you can see PS3 absolutly swamps HDDVD in volume, yet in disc sales, it seems to be 3-1 for Blu-Ray, 2-1 for Blu-Ray, a much lower level of domination than the PS3 sales suggest. I think the value of each stand alone player sold is mutiples higher than each player sold in a console, because the buyer of a stand alone, is someone who is targeting the format to play movies. In this way I see the X360 add on making sense. Only people who are actively interested in HDDVD's will buy this. This is why I'm sure the "attach rate" on HDDVD hardware is much higher than on Blu-Ray if you count PS3.
I look back to DVD sales. I'm not sure how much DVD playback ever helped the PS2. Of course as of today, it's irrelevant, mostly. There was a small window in time when a PS2 maybe had some added value as a DVD player, before DVD penetration became ubiquitous, but the price of the PS2 was necessarily pretty high at that point ($299).
I think Blu-Ray in PS3 will be fighting that same small window of relevancy, before Blu-Ray/HDDVD prices plummet. As of now the price of PS3 is very high, so I dont think it's wildly attractive as a Blu-Ray player. Meanwhile, HDDVD stand alone prices are dropping like a rock, should be a $199 player by this fall. You could say the same for Blu-Ray, I even wonder is Sony holding up the price of Blu-Ray stand alone's to make PS3 more attractive? Overall that would be a very poor move for the format if so.
The other thing that I think will work against PS3 Blu_Ray to a point, is HDTV adoption. There's going to be some percent of PS3 owners who simply dont own HDTV's, and to them Blu-Ray movies are useless.
We can also look at UMD, which kind of probably stigmatized the entire Sony console trying to establish a format thing for retailers in the near past.
Personally, I've never liked playing movies on my consoles, because I worry it'll wear out the drive faster. For example, I dont really use my 360 as a DVD player for that reason. I suspect that's more my own oddity though, and not anything the vaunted casuals would would ever think about.