I work in theatre, with shows that include video clips, and "live" video.
As much as possible is pre-recorded and set up in advance.
A theatre show will have a sound person, a lights person, a video person, and a stage manager, who keeps everything running, all working at the same time.
Possibly if Steve's presentation is handled in theatre style, when he is talking about slide A, slide B will be put up on a monitor, the video person will confirm with their notes that it is the next one in sequence, the stage manager will double confirm with the master log book in front of him or her.
Then when Steve clicks that remote, a light goes on, or a beep goes off, alerting the stage manager, who will cue the next slide, via a second cue light / audio alert and the video person will trigger it. (So if Steve miscues it, the stage manager will catch it and not trigger the next slide)
The stage manager and video jockey may also have noted down key phrases that Steve says which will alert them to upcoming transitions.
These people are complete professionals, and almost NEVER make a mistake in a live performance - they do it 5 nights a week for a living.
One theatre I visited recently had 500 lights, all independently controlled via computer. Took 3 months to programme them for a single 2 week show...
I don't know much how upscale conferences / large corporate presentations are handled, so Steve's thing could be different.
Hope that was enlightening..
cheers
.. RedTomato ..