It was going to happen sometime.
OSX will probably die by the time it goes beyond 10.9, and that will be fine. iOS is a leaner OS which will carry the portables into the forefront of the market. As the iPads become more powerful over the next half-decade, OSX computer sales will diminish drastically since most people won't need them.
iOS is not a leaner OS, it's only an overly restricted graphical interface to the iTunes store. If you want to do anything with an iPad, you have to use your credit card. We've seen the rise and fall of this business model before in the 1960s on IBM mainframes. Apple is trying to turn back the wheel of time and repeat history. The only question is how long it will take for the average iCattle to wake up and refuse to be milked.
It is interesting to see that this is not only due to iOS rising in usage, but OS X declining.
Let's face it: OS X was never a really important computing platform, it's always been a niche market, for many obvious reasons: Too expensive, too closed, no third party hardware vendors, no penetration in the enterprise/corporate sector. And the average Mac user has usually been a non-technical person with non-technical needs, so it doesn't surprise me that this target audience now moves on to something dumbed-down like the iPad and misses nothing.
Given that iOS is the dominant mobile OS worldwide, it's fairly obvious that a sizeable chunk of users will be Windows users as well. It's similar to the situation with iTunes penetration, I think.
The last time figures were released, Android was the dominant mobile OS worldwide, not iOS. And with Amazon now also being a player in the Android segment, those figures are going to change even more drastically in the favor of Android. In the end, open platforms always win over walled gardens.
Mind you, there's nothing wrong with only needing a thin-client device like a cell-phone or a tablet, but if you think they will EVER replace full computers, you have no clue what you're talking about.
Obviously.
Unfortunately, the other poster will be right. For most home users, iPads and other slates/tablets will quickly be powerful enough to be full computer replacements for THOSE users. In the end, Apple will only be selling real computers to registered developers and the rest will be buying iPads or next genereation MacBook Airs with iOS on them. That is very clearly where Apple WANTS to be. Millions of dumb terminals and credit card accounts that are locked into their content iCloud. The generation mainframe business model - with huge data centers instead of mainframes at the core and all terminals are connected over the Internet to it. Millions of micro transactions per minute, all pumping money into Apple's bank accounts.
It's a great business concept for Apple - until the bubble collapses and people no longer want to be locked in.