How close are store bought broths and stocks to the real thing?
There's a great deal of variation in the quality of the pre-made stocks you get from different sources, so there's no clear-cut answer. Here's the types you might find:


Stock cubes: these are dehydrated stock, or sometimes just chemicals meant to taste like it. It's the lowest quality option. There's a lot of variation here, I've found some brands (knorr for example) to be better than many others, but still not close to the real thing. I rarely use these
Stock powders: similar to cubes these are loose rather than cubed powder stocks. The advantage of them over cubes is they dissolve much faster
Gels: these are more recent, they are super-concentrated stocks in a gel format. They come in little mini tubs, you peel the lid off and squeeze/spoon the contents out. I'm not sure these have made it over the pond to the US yet. They are IMO much better than cubes or powders and closer to the real thing, and I use them more often than any other alternative
Canned/bagged stock: Most of the time these are concentrated, there's a lot of variation in quality between brands. They have a long shelf life, and don't require refrigeration
Fresh stock: you can sometimes find fresh stocks in the refrigerator section of the supermarket, or at a butcher/specialist food store. These are the best alternative but can be expensive


Personally I rarely make stock, and when I do I use it right away. When I need to strengthen the flavor of a broth, or I need stock I use knorr stockpots (one of the concentrated gel products), or if I only need a little flavor, I spoon of powder. There are a few cubes rattling around my cupboards for emergencies too.