Having said that, that was easier since it was running that day so I could hear it!
I think I walked it that day to save £2, so you can guess I'd never pay £15-20 for a cab
Beyond any personal inconvenience, and i have no problem walking, I'm thinking of the (hopefully) large numbers attending who will be expecting to be taken straight to the venue, many of whom may not be familiar with getting around London as it is.
Last time I went to an event only accessible via DLR with large numbers of people, I think i had to wait 2 hours after the event to get the replacement bus as there wasn't enough to cope with the numbers but that was some years ago.
Yes, there are other ways to get there but it will cause problems for a lot of people.