What does Wolfenstein being released as shareware have to do with anything? Last time I checked shareware was little more than an arcane term for what we in the modern world call a demo.
As far as whether mods are allowed by the creators of the game or not, lets all just be thankful that some game deves bless us with the privilege of creating free content for their games that keeps them alive far longer than they would have otherwise.
The problem I am seeing with Pushmo is they took a single simple mechanic and based the entire game around it. Literally its the lowest common denominator in what I am from this point on going to call the PixelPull genera. Simply put ..... it can't get any simpler.
So of course anything that uses it is going to be a "rip off" of Pushmo. Just like I could point to any of a slew of block breaking games and scream to the heavens that they are all blatant and shameless ripoffs of breakout.
Now if you don't mind I'm off to enjoy some Wizorb
"What does Wolfenstein being released as shareware have to do with anything?"
It was released with an open license to modify the code. Anyone could make their own version of the game, and they did.
Though today they seem to get used interchangeably, "shareware" and "demo" used to be very different things. Shareware was full software meant for free distribution, and including an unlimited license for use and modification, while a demo was, well, just a demo version of the software.
Today, some companies use "shareware" to mean "basic", which usually means "free, but with less features". That wasn't the case 20 years ago.
The thing about this Pushmo clone is that it's not just copying the basic mechanic of the game, it's also copying the aesthetic, and the game's rules and goal. Anyone can take the general, most basic concept of a falling block puzzle and make a game, but if you make it four-block shapes that disappear when lines are formed, you basically cloned Tetris.
Wizorb is a great example of "not a clone".
Block breaker used the most basic mechanic possible, much like Pushmo. Mind you I'm not huge into the Block breaker genera so I'm not all that familiar with games outside the original and Wizorb. I do however remember seeing slews of shameless block breaker clones when I was growing up.
If people were able to lock away the basic mechanics of a game like block breaker or Pushmo then games like Wizorb would never exist.
If it wasn't for those initial clones...
The point I keep trying to make is that clones happen especially when a game comes out in its simplest form like block breaker (use paddle/ball break blocks) or pushmo (pull blocks out get to top of pixel art).
I'm not saying that people should jump on the clone over the original. There is certainly nothing wrong with going out and buying Pushmo. The point is that blatant clones tend to come before innovation and like it or lump it they have a right to exist and as unsavory as the occasional blatant clone is the alternative is worse for everyone.

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