Here's a point to remember: Regardless of its stated purpose, every chain letter has only one real goal — propagation. In that respect chain letters are comparable to computer viruses, except they use human psychology instead of programming code to achieve the desired end. A "successful" chain letter combines a variety of psychological strategies to persuade recipients to reproduce it:
Emotional manipulation. There's always a "hook," reinforced with positive and/or negative motivators. In the present example, the hook is the sad story of a helpless little girl dying of cancer. For positive reinforcement, there's an implied reward: You'll feel good about yourself for helping out. For negative reinforcement, look no further than the subject line: "If you delete this you don't have a heart."
The promise of something for nothing. Every chain letter, whether it's for luck, money or charity, promises something for nothing. In this case you can supposedly donate money towards saving a child's life without sacrificing a penny from your own pocket. All you have to do is forward the message.
Gimmicks. Gimmicks provide seemingly reasonable practical explanations of how the stated goal of the chain letter can be achieved. There are two in the present example. The first is the claim that two prominent corporations have promised to donate 32 cents per forward (the largest sum yet for this type of chain letter, by the way). The second is the claim that technology exists which will automatically "track" the progress of the email and tally the number of forwards. Neither claim makes sense if you think about it. When major corporations make charitable donations, they're not likely to choose means as inefficient, random and ethically questionable as chain letters. As for "email tracking," the technology doesn't yet exist to permit the centralized collection of data on every sender and recipient of a randomly circulated chain letter.
That said, gimmicks are just helpers; they don't make the chain letter. These messages are nonsensical if you think about them, but whole idea is to properly tenderize you with emotional appeals so you'll click before you think.
Caveat lector. 
More about chain letters:
Chain Letters: From Snail Mail to Email
A brief overview and history
Further Adventures in Email Tracking
Genealogy of an Internet folk belief
Why Forwarded Email Can't Be Tracked
By Simon Slavin, Urban Legend Zeitgeist
Sick, Dying and Missing Kids in Netlore
A sampling of what's out there
Freebie Chain Letter Hoaxes
Another genre utilizing the fiction of "email tracking"
