(For the other side of this debate, visit my open source blog.)
It has to do with the nature of the industries.
Every device maker or drug maker has to win two government approvals to reach market. The key moment is FDA approval. Patent approval is a defensive measure, in which you're seeking a monopoly on the approved drug or device.
Drugs are generally protected by a single patent. You patent your particular compound, for whatever it's good for, then seek FDA approval for using the drug to treat people.
Devices may have multiple patents, but in any case the patents don't cover what the devices do, just how they do it. You can patent a mousetrap, but someone else can patent a better one.
Thus patent trolls are not an enormous problem. They exist, but they're usually more interested in finding a market than exploiting one.
This isn't the way things work in technology, where both software and business method patents, created by courts, may cover not just what's contained in the package but the very idea of what it does.
In years past we've had people try to gain patent protection for basic concepts like multimedia or the concept of reverse auctions, expressed in software, tieing up the entire industry in litigation.
Compromising those contradictory business models proved impossible. If technology wants industry-specific protection, it should stand for that and not try again to roll the medical industry.
So says the industry, and Congress reluctantly has agreed.