I ride on roads and paved bike paths fairly frequently and I periodically see a guy ride by and he will have about 15inches of seatpost sticking out of his frame. Other times I will see other guys that have their saddle flush with the frame and no seatpost sticking out.

Makes me wonder....

Does no exposed seatpost indicate that the frame is too big and the rider compensated by bottoming out the seatpost? On the other hand, 15inches of of seatpost sticking out would indicate too small of a frame, right?

Myself, I always end up with about 4-8 inches of seatpost sticking out. Can't help but wonder about some of the other guys I see riding around with 15inches or none at all. I understand that as long as it works, it works, but....

Depends on the frame. Different geometries will yield different amounts of post.

For reference:

More flexible riders will typically have a seat post way up.

If the stem is flipped up with a stack of spacers AND the seatpost is way up, then the frame is too small. If the stem is down with a modest spacer or two underneath, then it's probably just a rider with long legs.

The gravel, cx, and road look exactly the same to me.

I will say that of all my bikes the newest ones are the ones with more exposed seatpost. The steel road bike from the 1980's is the one with the shortest exposed post. Both are 54 cm.

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Top tubes slope at different amounts. A bigger slope means more post.
A good fit, is a good fit. The post height/leg extension may change a bit based on type of riding.
True, for seat in the same position more post/less post (and material and shape) does mean different ride, but there is no such thing as better riders have more or less post, only really bad fits where anything can be one extreme or the other.

On the straight top tube, the ball park reference was a handful of post between the saddle and frame. My bike complies.

On my sloping TT frame, there is much more.

I am surprised at how many cyclists I have come across that did not know there was a difference in top tubes.

Yes,I grabbed the first picture i saw with multiple geometry bikes in it.

The fastest bikes do not have sloped top tubes - or round posts. But they will be a bit heavier.

I thought the old "rule of thumb" for back-in-the-day frame styles was that the seatpost show should be roughly the same as the head tube length. Nowadays with compact and semi-compact frames, this is no longer a good reference.

Never heard that one but i look over at my bike and it looks true as well.

The amount of seat tube many road riders now show would have been seen as a sign of a frame that was too small back in the 70s.

you mean like this?