Can someone elaborate?

The idea is as follows:

Your VCR is a sequential-read mechanism. It can only look at a single frame of the videotape at a time. It's got no idea what's coming up, only what it currently sees in the current thing that is on the screen.

So, as a result, the VCR only has half of the needed information in detecting commercial breaks. It can only make a guess when the commercial break STARTS but not whether it ENDS any time soon, hence it gets faked out several times during each X-Files episode when the screen is black.

A hard-disk device like the Replay, on the other hand, can look at the ENTIRE SHOW as a whole unit. It can look at the patterns of black frames as a group. Based on what it knows about how commercials fill network shows, it can make a much better educated guess as to what's a commercial and what isn't. And here's the critical part: Because of this, it's able to choose to err on the side of caution, and if it's not sure about a segment, it won't even start a commercial-skip at all. So the 20% error becomes 20% commercial still present rather than 20% program material skipped.

See?