>6. Ad-exchange receives all the bids and picks the second highest bidder (no idea why it's the second highest)
>7. Ad-exchange then sends this second highest bidder's ad URL back to the waiting javascript running in the users browser, and ad-exchange marks the winning bid so it knows who won/who has to pay at the end of the month.
It's a second-price auction - the highest bidder is picked, but the second-highest price is paid (more or less). The URL thus is from the highest bidder, not the second highest bidder.
If you know of some way to swap out servers with 100% uptime, I'd like to hear it. Even Stack Exchange, which had that sort of plan in place, had to go 'static' for about a half hour.
Parsing is syntax. Interpretation is semantics. Just parsing JS just gives you information about its syntax, and any decent editor (like vim or emacs) has a programmable interface such that you can write a JS parser.
It's a second-price auction - the highest bidder is picked, but the second-highest price is paid (more or less). The URL thus is from the highest bidder, not the second highest bidder.