I don't know what office you work in.. but no; iPads have not replaced PC's. Yet. There are too many applications that just don't work well enough on a tablet device. This will change of course. But not today.
Granted a lot of people in the office have ipads, but most bought it themselves. And use it with a PC. Not in place of.
We've been talking a lot about replacing everything with iPads. The install price for the customers would be much much cheaper, and the experience for all involved would be better.
The only thing holding us back, is the lack of available man hours, to make the switch, but it will happen.
(Edit: added "something like")
The bonus of using iOS, is predictable behavior, sleek design, better custom accesories (iPad msr) , percieved value of the customer, but also the ability to get a replacement device, with ease.
If you go with Acer X, you have no idea of availabilty 2-3 months later, let alone a year or two.
Is deploying a custom application to the iPad (without going through the App Store) as easy was sideloading to an android device?
However, if you would rather sidestep the regular appstore, Apple provides something called the Volume Purchasing program. With that, it is possible to provide apps directly to devices, either for free or a paid solution.
So IMHO it's not that far fetched to say that individuals and businesses are buying less PCs than they were when Win XP came along. Doesn't say they aren't buying them anymore, just less.
The only place I see people using their iPads to cash out are at the farmers market. And that makes sense since you are outside and need something portable.
But I do agree, businesses are buying less PC's but not because they are replacing them with iPads. Because they aren't spending the money. The glut in the PC market is that everyone has one. It's saturated (I'm talking the Western World here, not developing countries). Now you buy one as a upgrade. And businesses only upgrade when they must.
MS's job is to provide a compelling reason to upgrade. Time will tell if Windows 8 does this (I doubt it actually. Maybe when more apps are built for it).
the comment above you also talks about 'tablets', not 'ipads'. Tablet-style things (ie rather small devices with a touch screen) have been used for cash registers and as controls in the industry for quite some time. A lot of them were merely PC's, running some sort of Windows. This might start changing now since tablets are getting more widespread, hardware getting cheaper etc.
Which must be a pretty slow cycle in this space. I recently shopped at a store that I hadn't been to in at least a decade. I was shocked to find they were still using the exact same orange screen terminals that they were using when I was a young child.
That doesn't necessarily invalidate the original claim though. All new POS terminal installations could be using iPads or similar tablet devices.
Imagine trying to effectively generate an excel sheet. I cringe at the thought of trying to manipulate data from a tablet. You would waste a lot of time to produce something sub par. This is one example, there are many more.
Although apple reinvented the tablet market it will take greater innovation and the creation of some other tools before tablets become effective and efficient machines in the work place.