I downloaded a free asset from the orbolt marketplace called legoize, which is a variation on the brickify tutorial project. I was expecting to be able to look at it and learn how some of the extra features were done, but when I bring legoize into my scene I can't dive down into the network, it gives an access denied warning.

Is that something I can expect from all orbolt assets? Or is this a choice the author made when they uploaded to the store? I am assuming this is intended behavior, or maybe there's something going on that's preventing me from editing the network when I should in fact be able to do so (I'm having some other issues with digital assets I've created currently so I'm not quite certain of anything atm).

Orbolt assets are locked by the asset creator by choice. Sometimes they are left open. Sometimes the free version is locked and paid version open. Its a feature to allow HDA creators to protect their work. You can blackbox assets from within Houdini also:
Assets–>Create Black Boxed Asset from Selection.

Careful to keep your editable asset file, you wont be able to open the blackboxed version.