I don't think that really matters, as they seem to be selling well enough. I'm not saying they should have done the same package deal they do now for the Premium if they sold it as one unit, but I do think they should have had the HD in one package starting at... say... $360.
They could have not bothered bundling the wireless controller or headset or component cables in and concentrated on the important stuff, and simply push the price down a bit ahead of schedule. (It's not like it will take any talent to "beat" the PS3 to those price points.) Not to mention the savings that would come from smoothing out the production and distribution process.
Unless the sales ratio of the Core is actually substantial compared to the Premium (and I have no hard numbers, but I think not--especially what with store employees pushing the Premium and badmouthing the Core the way I've seen), I think the monetary difference would be shruggable. Certainly not worth the downsides of forcing themselves and others to code to NOT having the HD, try to fit within the confines of a 64MB memory card, lacking backwards-compatibility, etc.
Just plain pointless, IMHO.