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While I would fully expect Apple's authoring software to support both HD optical disc standards, I will be quite surprised if Blue-Ray isn't eventually the standard optical drive included in non-BTO Macs.

That said, there will certainly be options to connect HD DVD drives externally to laptops and iMacs, and perhaps even internally via BTO ordering. Obviously, Mac Pro users can install whatever they wish, internally or externally, with ease.
 
Blu-Ray/HD-DVD will be available as a BTO option on the Mac Pros long before any other Apple system if Apple chooses to adopt them.
Apple's insistance on the slim, slot-loading laptop drives on every other machine is one reason.
Apple will choose whatever suits them, basically when it comes to whatever the media is.
 
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