Google crawls somes sites more often than others. This has been experimental - and for a while they were adding what is known as a "freshness" tage to listings.
This, as someone pointed out, is not the same as updating the index. You were pretty much listed in the same order. Google updates approximately once every 26 - 35 days. Next update should be around January 24th - February 6th.
The sites it crawls more often have nothing to do with Metatags - they have to do with PageRank (something similar to link popularity).
It takes about 4 - 6 weeks to get a site listed in Google. Submitting to Google does not help you. You must have links too your site from other sites in Google.
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