Cheap machines use pressurized portafilters or pressurized baskets for two reasons. One is that the assumption is that by buying a machine in that price range you probably aren't getting the most articulated grinder. So added pressure in the PF or basket will help get crema out even if your grinder sucks. The other reason is so they can accept ESE pods. To answer the other part of your question: as beans go stale some of their components break down (the crema making components especially).
Nice video to explain the crema of espressos. However, one bar equals one atmosphere or 14.5 psi, not 8.8 atm or 130 psi. That's the pressure the espresso machine uses!
Awesome video, but like others in the comments, carbon dioxide is also a very large part of what makes up the crema. This is why more freshly roasted coffees output more crema: there's more CO2 gas from the roast. As the coffee ages, it "degasses" which is why old coffee has less or "thin" crema. Also I think it's important to note that crema tastes horrible. It sure does look pretty, and I suppose it's a natural cream of the coffee, but would not recommend using crema as your creamer haha
