I decree that it will be the policy of this administration that the PS3 is indeed a Blu-Ray player. Conversely the hd-dvd add on will be counted as a hd-dvd player.
Seriously people devises are converging. What is next? Are the Tivo freaks going to bash the PS3 when it gets DVR functions? Are the iPod hounds going to bash the iPhone as not a true iPod because it can place a telephone call?
One flaw with your policy:
the HDDVD add on is purchased for ONE thing, playing HDDVD's and can be fairly counted. The PS3 is a media center and has numerous functions therefore you cannot fairly count them all for attach rate. You cannot also fairly exclude them all.
This is why attach rate is more FUD and total movie sales is all anyone should give a SHAT about.