"I think there should be limits on the power of software companies though. Undeniably, software is not a concrete asset which has intrinsic value, and anyhow, companies should not be allowed to hold users to ransom with exclusively rental systems, obstructive market tactics and plain shoddy products."
When you say "should not be allowed", what do you mean? Should not be allowed by whom? If Levi's jeans wants to move to a rental model from a sale model should they be disallowed by government? If not, why should Microsoft be disallowed? Should Levi's be allowed to sell shoddy jeans? If so, shouldn't Microsoft be similarly allowed?
"As a final thought: What (besides paranoia and critical trade secrets (ie: paranoia) -- NB: piracy is going to happen anyway) is to prevent the release of full or partial source as part of every package, regardless of pricing?"
I'm in favor of wider availability to source code but there are reasons a company might choose otherwise. One is algorithmic secrets (trade secrets is too strong of a word because binary code can be reverse engineered).
Another is embarrasing comments in the code: "this really sucks...fix it later." Another is indications of future product directions. Another is security through obscurity (which is sometimes better than nothing). A company may also wish for their customers to think that their product is more complicated than it is (especially if it was developed in a high level language or uses some other similar advantage).
Finally, a company may want to have exclusive power over upgrades and fixes. You could imagine a situation where a competitor to Microsoft Word starts out as a series of patches TO Word. Over time it grows into a genuine competitor.
If the advantages of source to the user are strong enough then vendors may one day be forced to give up these benefits of closed source in order to satisfy customer demand. But customers seem not to care much.