Not sure what you are getting at with your question Mike. The other two posters provided some more info.
Each track system is as you say "all it's own." But you can match them (with a little extra effort), some brands easier to do than others. For example, Gargraves brand track is the same height as tubular 027 track and mating pins are available.
To add to what the other two guys said, you can use differing brands of 027 track together: You have MARX, Lionel, K-Line and Williams by Bachmann, plus a few obscure others. There's Ives and there was a Japanese firm making 027 track and switches.
In additional to the standard 27 inch radius of 027 track, there's also 42 inch and 54 inch that were made by Lionel. Lionel also made matching switches for the 42 inch radius. Not sure if for their 54 radius curves.
MARX also made a 34 inch radius curve in 027 profile. I don't think they made matching switches for that radius though.
The 0 gauge tubular track has even more curve options, especially now with Menards offering tubular 0 track. You'd have to check their website for the options. I think they have a 36 inch diameter 0 gauge curve, which no one has ever offered before.
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Not sure what you are getting at with your question. Are you trying to build a layout and considering which track to use?
As you might realize, tubular 027 and 0 gauge track are now out of production, save for Menards new offerings in 0 gauge, and what is left in inventory from Williams by Bachmann (It's anyone's guess what Bachmann is thinking with their Williams line of trains... not looking encouraging though).
There's still plenty of tubular track out there, but you probably won't be able to call some dealer and get everything you need. You'll probably have to use several dealers. One dealer I looked at was out of stock of 42 inch 027 curves, but had 54 inch in stock. He had 42-inch switch tracks, but not in both left hand and right hand.
As a rule of thumb, the larger radius 027 curves and switches will be harder to find, only because it wasn't made for as long a period of time. That and it was popular when introduced. Another example: K-Line made a low profile switch with a very small switch box housing (when compare to previous K-Line and Lionel 027 switches), but those are getting harder to find. Not impossible, but not as easy as just calling a dealer and ordering a few of them.
Hope all of this helps you out.