paddy_36, I'm glad I made sense with this question - some answers are not easy to simplify.
You will find that bubble baths and shower gels do contain the same ingredients as you've found and Supernick has verified. There are two reasons why people usually think that bubble bath is more concentrated.
The first is that in many cases bubble baths are more highly coloured than shower gels making them look "stronger". The reality is that the manufacturers simply add greater quantities of artificial colours to make them look that way.
The second reason is that bubble bath manufacturers add more salt to the product than they put in their shower gels. The more salt they add, the thicker and more viscous the product appears. Now, when you think about, doesn't a thicker product appear stronger and more concentrated as well? Do you see how easily these manufacturers can manipulate the mind!
The huge quantities of salt these products contain do not really cause any harm as they have limited contact with the skin before being washed off or diluted. There has been little development in formulations of these products for years and as a result no real adverse effects have been recorded and they are generally regarded as safe. All the same, you will always find the odd person who is allergic to one or more of the ingredients.
Supernick is right when he says the same ingredients are used in generic and branded products, WaldoMcFroog is also right when he says that manufactures are failing to alert the public that their products are the same thing. They have been known in the past to put extracts of expensive perfumes in some branded products to make them seem more exotic and of a higher quality than the standard types and of course, they thicken them more.