If you are playing a NL cash game you can bet any amount in front of you at any time. If an opponent has 50,000 and you only have 12, your opponent is allowed to jam the entire 50,000. I don't see how this is different than a tournament. If you are at the final table of a big tourney and you are the short stack, you have to battle back from that.
Now most cash games these days, at least a low limits, have a max buyin that is usually 100 big blinds. The difference you get in cash games it let's say we are playing and we all buyin for the max and I bust 2 people in the first hand. I now have 3x the max buyin and you still only have your buyin. Where cash games differ from tournaments is that these 2 players that went busto can now buy in for more chips. They aren't out if they don't want to be.So if you started with 9 players you now have 11 "buyins" on the table. And it can keep going up from there. And often does :-)
In the same way, there is no requirement that you stay at the table for any length of time. if you quintuple up on your first hand and you want to cash out, there is nobody stopping you from doing that. Sure you may get some heckling from people about running away with their money, but it isn't their money anymore. It's yours. :-)
Also, play money is, well, play money. It doesn't matter to a whole lot of people. To play poker you need to play for something that has meaning or value. My family in general takes game playing seriously, so while play deviates from good when we play for low or no stakes in family games, it doesn't deviate much. Some people just jam their whole fake money stack because they can and it doesn't mean anything to them. It makes playing the game suck. I don't think there's anything you can do about that.
Lastly, if it was real money and you put out a bet of 40 and it was 1/4 of your stack and somebody with a monster stack could push all in, they probably would. If you are severly short stacked against an opponent and you make a bet, you need to be ready to make the same sort of decision you would in a tourney where before you bet any amount, you need to decide what to do if you get called or re-raised.
There are what are referred to as cap games, which is what it sounds like you are asking about. These are usually reserved for higher stakes games, where you can bet any amount from the big blind up to the cap in a single hand. If say you were playing 1/2 NLHE with a 200 cap. In a single hand no player could bet more than 200. If you were first to bet and bet 40 in this spot, the most that you could get reraised would be an additional 160 to bring the total bet to 200. At that point the other players options are to call or fold. No more reraising is possible. Here is a brief explanation of how cap games work http://www.pokerlistings.com/c…..mes-part-1