:-)

death perpetrated by someone on purpose ie murder at a distance

If the phrase "death by design" is used correctly, it refers to the characteristics of a "thing" or possibly an "entity" -- without more context it is hard to tell exactly which it is in your case -- that make it fail.

You will find if you Google the phrase, numerous references to mechanical things that fail because they are designed to fall apart after a period time. You will also find references to medical papers that suggest that certain cells are programmed to decline in a certain way and at a certain rate.

Examples:
http://www.evoyage.com/JoshMitteldorf.htm (he claims that evolution is a sort of planned obsolescence)
http://magazine.uchicago.edu/9606/9606Celldeath.html (about cell death)
And more at http://www.google.com/search?hl=en&lr=&q="death by design" -...

In your context, it could be that the author is making some sort of a statement about long-suffering people people and suffering that results from illness and suffering that results from the way those people are designed (or even the Grand Design of things). Since I don't have your context, I can't determine if the author is drawing a contrasting relationship, a causal one, or an interdependent one.

gets not a few googles, infers that the person who wants to croak decides how and when it is to take place

This is my guess only. Someone who doesn't feel like living, someone who feels perpetually unhappy, someone "luckless," someone who always seems to attract trouble and sickness...that someone is subconsciously/unconscioulsy intent on not living, or even intent on dying. "By design" means "by intent". The nature of intent/design is unknown here. I've known some people who seem to be besieged by an unending set of troubles. After years of attempts to help them, one understands that they don't want/don't know how to be helped/receive help. It may have a deeper psychological meaning - such as low self-esteem, self-destructive tendencies, or a mere habit of being sick that "habituates" one into not feeling quite normal most of the time and lacking the will to live. I don't know and I certainly don't claim that I know anything in this respect...I've just encountered such people whom trouble and sickness doesn't seem to leave alone...And it makes one wonder...

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Note added at 5 hrs 55 mins (2004-10-17 05:33:55 GMT)
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http://www.evoyage.com/JoshMitteldorf.htm this is a link that explores the biological possibilities. Without knowing your text, it\'s hard to judge what would be suitable, but I am sure that you\'ll be able to choose.

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Note added at 16 hrs 14 mins (2004-10-17 15:53:29 GMT)
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Here is another version of \'death by design\" - something that is built into the system that is designed to kill, and in Deborah\'s answer above this phenomenon is also mentioned. Here\'s the reference about the biological death-by-design, a biological program, so to speak: http://research.unc.edu/endeavors/win98/dangl.html