Because it's broken. Without more details, we can't be more specific.
The HP touch screen is made of two very thin transparent layers with a thin space between them. When someone touches the screen, the two layers touch to become connected and what has been touched can then be read.
HP PW460T 12 MP, HP PW460T 12 MP, HP PW 360TB 12 MP and HP PB360 12 MP are touch screen HP cameras. They are well within your budget, going for $100-$150 each.
The touch screen feature requires either a screen or a plate(digitizer) you put in front of the screen. Then the touch inputs can be received by the computer via USB(Serial in the old days).Some of the systems can use a camera or IR led's(early HP touch smart PCs) to see your finger location as well.
HP Touch Smart 9300 Elite is the best all in one computer in the market. The large, multi-touch screen is ideal for customer interaction, and intuitive and convenient for visually intensive applications.
There's many benefits of using an HP touch screen especially the interaction during games. It allows users to interact with the computer directly and it's helpful for navigation.
It takes about a week to get completely used to and comfortable with the touch screen.
Antonio Vivaldi - The Four Seasons, Summer
The HP Pavilion TX2000Z 12.1" TOUCH-SCREEN NOTEBOOK LAPTOP PC is more durable than some others
They used to make laptop that are 15' with touch screen. However, they stopped year or two ago. The laptop was called HP Pavilion DV6t Select Edition. It gives you option to add touch screen. Like I said, they removed that option. They still sell the laptop. But removed touch screen and backlit keyboard.
The most popular brands of touchscreen laptops in 2012 were Acer, Toshiba, Asus, Sony, Dell, HP and Lenovo. So far the Lenovo IdeaPad Yoga 13 gets some of the best reviews for touch screen laptops.
According to HP, it has a "Multi-touch glass display with a special coating for easier cleaning and abrasion resistance".
This answer is an oppinion..... in my personal oppinion i think you should get the touch smart rather than the IMac. I just think the TouchSmart brings something new a better to the table because of the extra feture, the touch screen! ( I really want the TouchSmart IQ770 ) Hope I have helped!! : )