1.) Industrial 9V's (like ProCells) are truly the same battery that's just been repackaged to convince the consumer to pay more. The ProCell has an IDENTICAL voltage curve to a standard Duracell.
I agree with you that an industrial battery's voltage curve is exactly the same as a regular 9v battery, and that they are built the same way (they are both alkaline batteries), but with one major difference. At the bottom of a regular 9v battery is a cardboard spacer. An industrial 9v has no cardboard spacer at the bottom, and instead uses the extra room for more active material, providing a longer battery life. The voltage, in this case, isn't the difference at all.
Duracell, for this reason, does not want its ProCell line competing with its normal consumer lines, and deliberately puts this on the battery packaging. They are clearly marked as "not for retail sale," and it is a violation of a company's agreement with Duracell for the company to put it on a salesfloor, easily accessible to the average consumer.
Most places that have them available for purchase have them under their commercial/governmental pricing tier, and they are more often than not less expensive than the regular consumer line.
A sleep doctor that my company supplies ProCells to was using the regular consumer line in the monitoring equipment that he sent home with patients to collect data while they sleep at home. On average, he was getting 5 or 6 hours out of the batteries, which was interfering with his work, because he needs a full 8 hrs. of data. Once we set him up with the ProCells, he started getting between 9 and 10 hours, on average. This is just one of the many stories that our customers have told me about the ProCell line.
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Lithium and rechargeable batteries are a different beast altogether.
An alkaline 9v battery is made up of 6 alkaline cells comprised of 1.5 volts a piece, wired in series (=actual 9v).
A rechargeable "9v" battery is made up of 8 cells (NiMH, or NiCD) at 1.2 volts a piece, again wired in series (=9.6 volts).
A lithium ion "9v" battery is, as you've probably guessed, made up of lithium cells, which are normally rated at 3.6 volts/cell.
The PowerBug website shows this, as well, and it is true. So yes, the voltages are different between the three styles.