(1) … the date that a domain with which a document is registered may be used as an indication of the inception date of the document.
(2) Certain signals may be used to distinguish between illegitimate and legitimate domains. … Valuable (legitimate) domains are often paid for several years in advance, while doorway (illegitimate) domains rarely are used for more than a year. Therefore, the date when a domain expires in the future can be used as a factor in predicting the legitimacy of a domain and, thus, the documents associated therewith."
Matt doesn't say it's not part of the algorithm but he gives the idea it's not that important.