Uno is just a corporate spinoff from Mao anyway. I believe thats why they don't like house rules, once people go back to having fun with cards making their own rules they no longer need a product.
Who actually plays it that wrong way, allowing stacking of +4 and instead of taking four and being skipped you place and +2 and the next person get six?
The rules are not ambiguous. This sounds like a silly "house rule" at best with clever marketing being more likely.
It makes the game exciting for the first two or three times the strategic thing happens. Then it is extremely tedious and boring. I once witnessed a game with all the house rules at a party. People just started to look around for someone to give their hand to, as they were missing the rest of the party. The game went on for over two hours at which point none of the players left had started the game. Eventually everyone just placed the cards on the table and walked away. It got just too mind numbly dull and mechanic. There's videos online of uno games that lasted over 6 hours because of these rules, and they're absolute torture.
I have nothing against house rules, as long as they are balanced and fun for all players. But the typical house rules are created by overtly competitive players who want to optimize the fun out of games and maximize their potential for being cruel towards other players.