I think especially beginners who learn from snippets and various sites often use code that is simply outdated and/or bad. They don't know any better so they use what works.
A few months ago I had the same requirement and felt many of the existing services were providing more than I actually needed or wanted. That was basically the reason for why I created a small bash script and later on in December built a web application around it. I just launched it 3 weeks ago so I would love to get a few more people to check it out.
I think the content is just not finished yet. You can view the preview at http://preview.python.org and there is still a lot missing. Do you know who is in charge of the redesign?
From my personal experience I would suggest working with PDO. It is easy to implement, supports multiple drivers if needed and has named parameters in your prepared statements. The difference in terms of performance should be insignificant - although I think in some cases mysqli tends to execute faster.
Well, it's Themeforest. I agree that their rejection reasons often seem generic and somewhat random but with the amount of submissions they receive it is understandable. As I said, if the quality is right and you somehow stand out from the crowd chances are pretty high it'll get accepted.
No, I am selling through a very well known marketplace which will get a cut for each sale. In my opinion it is much easier to start with due to the high reach of potential customers you will get. As soon as you built a customer base you could probably consider selling the themes on your own site.
There sure are people making enough money to live of selling themes and templates. I myself created a couple of WP themes almost two years ago and can still live from the revenue. I am however enrolled in university so my costs are significantly lower than they would be as a regular freelancer. The costs of living are always relative as to where you are in your life, your lifestyle and of course where you live. Someone living in a country where the dollar is much stronger than the local currency has a big advantage. What is also often forgotten about are taxes and insurance. You always have to have a little something saved up if a problem should arise.
If you have a solid code base, a few creative ideas and good graphic skills you can still make quite a bit of money. Of course it is always important to find a niche in the market that is not as over-saturated as others. But that basically applies to any other business.