If you think about it a strict HTML 4.01 or an XHTML document is more modern, more 'valid' more accessible more on the WC3 bandwagon and harder to accomplish (more skill required) than a "loose" or "Transitional" Document. Assuminf that all these ducument validate properly in their respective category.
Would Google Algo give brownie points for!Doctype?
How much would this weigh in the algo?
I'd like to hear some opinions on this.