I don't think investments make your earn this much at all. Unless you've invested a huge amount of money, investments wouldn't help you that much. It can help you in the long run, but most of the time the payment per week of an investment is really low. 0.1BTC can be achieved by having a job, doing tasks for others, etc. You don't need an investment at all.
Just like you said, he/she can earn 0.04BTC per week in a signature campaign. There was no investment required on that and it pays much more than an investment. A little more 0.06BTC worth of work will enable you to reach the 0.1BTC. That 0.06BTC can be consists of freelancing, buying and selling, photoshopping, creating a logo, managing a signature campaign, etc. No matter what it is, you would most probably have to add two or more tasks to reach 0.1BTC per week.