The college I go to tried upgrading to windows 7, but went back to XP because the systems were slow on windows 7.
When you have a bunch of computers with 2GB ram and a pentium D (or at best, an entry level core 2 duo (still with 2GB of RAM), things run slow.
The problem is that for most windows XP users, upgrading to windows 7 also means buying a new computer which is a hard sell if their current computer is doing everything they need right now.
If you don't need some of the newer features such as direct x 11, there is not much of a true need to upgrade.
On a modern low cost system, windows XP can offer SSD like boot speeds on a standard hard drive. menus and other OS assets perform with SSD like performance also. It is just a lightweight OS that uses less RAM that uses a fraction of the RAM that even android uses (on a clean boot windows XP can use as little as 40MB of RAM, and it really only has to load that amount of data to get to the desktop.
In a quick video I did a while back I showed the boot process of windows XP on a clean boot, on a virtual machine (which adds a performance overhead)
http://www.youtube.com/watch?v=gLsNxKjp9L8
Now lets take a look at the system requirements for windows XP
Pentium 233-megahertz (MHz) processor or faster (300 MHz is recommended)
At least 64 megabytes (MB) of RAM (128 MB is recommended)
At least 1.5 gigabytes (GB) of available space on the hard disk
CD-ROM or DVD-ROM drive
Keyboard and a Microsoft Mouse or some other compatible pointing device
Video adapter and monitor with Super VGA (800 x 600)or higher resolution
Sound card
Speakers or headphones
The OS was very IO friendly (it had to be, as this was the type of storage world it was entering)
http://www.xbitlabs.com/articles/storage/display/wd400ab.html
Fast forward a couple years where hard drives are doing 120MB/s+ and massively better IOPS and 4K performance, and you get a rather speedy OS if you can avoid bloating it.
If windows XP supported trim, 64 bit (properly and not the crap implementation on windows XP x64 which has an insane performance overhead when emulating support for 32 bit applications), and the latest direct x, I would still be using windows XP
On top of all of that, for businesses, they may be using older software that may not be properly supported on windows 7. So being realistic, how convincing will it be for a business to buy copies of windows 7 or 8, and likely buy new computers to handle the OS, lose compatibility with some old applications that are no longer updated, all to do the same thing that they were doing before on their old systems.
Keep in mind that old is not a reason to upgrade. Old is a justification for a lack of something. For example, why doesn't Why don't cameras from the 1920's have an LCD screen? because they had not been invented yet and thus the device is too old to have had one.
Most arguments that claim that XP is too old, have no way of justifying how it is too old. The wheel is old but we still use it.
Windows XP is also largely just as secure. Virtually all security based patches are released for windows xp, vista, 7, and 8
and that is due to the fact that programmers of these operating systems, do not intentionally design it to be exploited. Meaning exploits will impact multiple versions of the OS. To see for your self, look at the security updates for for the patch Tuesday for windows 7 and windows pretty much more than 90% of the time the same security issue will be on both OS, the vast majority of the rest will be security exploits unique to vista, 7 and 8 due to new features they added which are being exploited.
And many security issues unique to XP are unique because a feature that was present in XP but not vista and up, was exploited.