The numbers you're comparing are not "poll results", they're odds of winning based on the polling.
The details of their models are spelled out here. They summarize them as:
Polls-plus: Combines polls with an economic index. Since the economic
index implies that this election should be a tossup, it assumes the
race will tighten somewhat.
Polls-only: A simpler,
what-you-see-is-what-you-get version of the model. It assumes current
polls reflect the best forecast for November, although with a lot of
Now-cast: A projection of what would happen in a
hypothetical election held today. Much more aggressive than the other
Then, they even have a section called "Differences between polls-only and now-cast":
- The now-cast is basically the polls-only model, except that we lie to
our computer and tell it the election is today.
- As a result, the
now-cast is very aggressive. It’s much more confident than polls-plus
or polls-only; it weights recent polls more heavily and is more
aggressive in calculating a trend line.
- There could be some big
differences around the conventions. The polls-only and polls-plus
models discount polls taken just after the conventions, whereas the
now-cast will work to quickly capture the convention bounce.