"Ink cartidges are a commodity. Just as there are many form factors of copy paper (letter, A4, cardstock, etc.), there are many formfactors of cartridges -- yet cartridges are routinely available from many vendors and, many purchasers including myself care only about form factor and price."
This is exactly what HP and Lexmark must avoid. If ink jet cartridges become a commodity, then their entire business model falls apart.
By purposefully designing patented (and copyrighted) technology into their ink-jet cartridges, HP and Lexmark can prevent them from becoming commodities and can charge high prices for ink.
It is the same approach that Gillette successfully uses in designing their razor blades - and frankly I am surprised that more companies do not do this.
It is hardly a new idea. Ironically, it was a socialist, King Camp Gillette, who came up with the concept in the late 19th century.
Gillette, HP, and Lexmark have built massively profitable businesses using this basic approach and so can many others, if they just plan and think intelligently BEFORE rushing off to develop a product.
This is called "patent engineering" and it is what my consulting business is specificially directed to produce - IPR strategies that support business models.
It is not enough to simply file patents on inventions and hope you have what you need. This is not a strategy for business success, it is a strategy for making patent attorneys wealthy.
To be successful in business, you must decide a priori what inventions you need and then invest research money into developing - and then patenting - those specific inventions. Without an IPR strategy to guide how research money is used, a business is simply betting on luck.
It is all explained in my booklet "Practical Patent Strategies Used by Successful Companies" http://www.althosbooks.com/prpastusbysu.html
Using the concepts I discuss, you can improve your chances of business success many times.
Lexmark tried to use copyright to protect an article of manufacture, which I personally think is improper, but before the 6th circuit rewrote the law, it appeared perfectly acceptable within the 4 corners of the DMCA. As I said Lexmark's IP department should receive full marks for using every aspect of intellectual property law to protect their business.
As a final remark, being old enough to remember when dot matrix printers were state of the art, no one can say that this aforementioned strategy stifles innovation, or is bad for consumers. The fact that I have a quiet, fast, 1200 dpi color printer on my desk is an innovation that has brought substantial benefit to me and others.
And I try to keep this in mind when I pay 20 evros for a replacement ink jet cartridge......