Imagine buying a laptop with an internet subscription for two years. If you happen to go on vacation or move countries, or sell your laptop to buy a new one... well tough luck you're still paying for that, usually non-transferable, contract for service you're no longer using. You can apply this to anything, like buying a television with a two year cable contract, it's just silly.
That model worked years ago. Today we're seeing customers on the move much more, and I'm personally seeing more turnover of equipment, too.
It doesn't really have anything to do with 'discounts'. Vendors weren't running a charity and they're not ending any discount, they're simply structuring everything a little differently, I think that makes sense.
Part of this trend is probably both consumer-driven (I wouldn't be surprise if this was a response to a growing number of consumers requesting and complaining about ending long-term contracts for sensible reasons like switching phones, country or even simply carrier), as well as driven by changes in law.
For example here in the Netherlands, a discounted phone is now seen as a loan. And loans have certain legal requirements. For example when you advertise or offer a loan, you must very visible (like a cancer warning on cigs) say 'Attention! Borrowing money costs money', which links you to a government initiative to inform about the risks of loans. Another requirement is that the vendor is transparent and clear about the costs of the loan, and it's in a standardised format that is very hard to structure in a way that it looks really good but really screws with you (like US payday loans). The loan must also be checked against the de facto debt-service coverage ratio of the individual if it's high enough, and then gets registered. All these things happened recently in response to the learnings from the consequences of predatory loans in the financial crisis.
And it is a loan, if you get a free phone but pay a higher monthly fee, it's not much different from buying a house on a mortgage and paying a monthly fee, only it's smaller in scale and timeframe. Because of this, the phone and the data plan are advertised separately, even if they're sold as a bundle. You can still get a phone with $0 upfront, but it's advertised as a loan transparently and separately from the dataplan. I wouldn't be surprised if stuff like this becomes a best practice standard worldwide pretty soon, and so perhaps carriers are making changes ahead of time.