I think that is probably a big part, but a bigger part is 90% of people in first world countries (who have money to pay and are valuable to advertisers) have never known how to use a computer (too complicated/scary) and now they all have one in their pockets they are addicted to. And since they never used computers they aren't as immune to being scammed, ripped off and fooled with fake dreams as us who lived through it all for years.
What makes your conspiracy theory about addicted developed-nations computer users more likely than the fact that strictly more human beings live outside of developed countries than within them? Are there any priors here? Is this a question of revenue per user? Is it a matter of cultural affinity? Is there any reason at all to discount the theory of more humans in developing nations?
A typical software development shop is still going to have more options for profitability primarily aiming at first world markets. And it's not even just because the customers have more money - regulatory challenges and difficulties navigating political realities in 3rd world countries make it hard to target new apps at such markets. My previous company had exactly that challenge - we focused not only on mobile- only but older/lower spec devices hoping to break into developing markets. They never succeeded and ended up releasing exclusively in Aus and UK, where many customers would actively prefer to use desktop-based interfaces.
Many developing markets don't necessarily have devices that are much older or lower spec. Look at Malaysia, Singapore, India, China, Taiwan etc. Many people upwards of middle class in these places have good access to reasonable devices.
Rather, they have different user behaviours and different needs. Success in these markets is about responding to customer needs locally, and not presuming that conventions, ideas, and designs that make sense in rich western countries make sense in those markets.
I've seen some good arguments that GUI layouts should be completely reexamined in developing markets, because the realities of differing languages (top to bottom, or right to left reading), or differing conventions in the presentation of information (extremely dense, or extremely sparse relative to what we are used to) mean that many app GUI's are completely counter intuitive and difficult to use in these markets.
Uber for example failed to succeed in India and Singapore because they couldn't adapt to the local markets need to pay in cash. Even though credit cards are available, many customers prefer to use cash. It was such a strong preference that they would rather not use Uber than pay for their taxis with credit cards.
We never even got past the regulatory hurdles and commerical agreements needed to launch at all.
Btw I would hardly consider Singapore or Taiwan developing markets - we were targeting a few east African nations and had pretty good stats on what devices were common (hint: definitely not the latest iPhones!).
