Well, I found the answer to my main question on the Delta website:
http://www.delta.com/skymiles/about_...ndby/index.jsp
Originally Posted by Delta.com
The Same-day Standby Option is available to Platinum and Gold Medallion® members only. Travel companions, family members, etc. are not eligible.
This program is not currently available for SkyTeam elite members or Northwest Airlines and Continental Airlines customers with equivalent Platinum and Gold Medallion status.
So standby is officially not available (at any price) to those who are not higher tiers in the Skymiles program.
Very sad. Another negative factor to consider in deciding whether to book Delta flights even if they are cheaper than other Skyteam airlines for a particular trip.
Still wondering whether, in recent experience, Delta gate agents are willing to book one on an earlier flight if they have room and someone shows up at the gate without checked baggage. Or whether they'd rather just keep those seats open to protect the integrity of their product.
