In answer to the stated, rather than the implied question, the thing you're talking about is known as Planned Obsolescence. There are all sorts of indications that it happens sometimes. Admittedly, wikipedia is a very weak source, but the fact that there's an in-depth page on the practice, with a significant number of references, breakdown of different subtypes, and some historical analysis seems like a fairly reliable indication that it exists as a thing and is done sometimes in some places.
for a couple of more specific, reliable links:
Consumer Reports talks about a HP making a $5M settlement WRT printers that consumed ink cartridges more quickly than they should have.
The initial proposal (back in 1932)
IEEE talks about an early case, generated by collusion between major lightbulb manufacturers
Overall, it looks like in the current day, companies tend to avoid obvious cases of self-sabotage. Evidence suggests that it still happens (as in the case of HP), but is relatively rare, perhaps because they're punished (by the consumer and/or legal system) when caught. They're much more likely to degrade things in more subtle, defensible ways. In particular, a number of modern alterations offer some defensible advantage or other (slimmer, lighter, or whatever), while making repair and maintenance more difficult or impossible. Still making their product shorter-lived in order to reap the benefits of more frequent replacement, but in a manner much easier to explain away.