I don't think a serial interface (which is what almost all dive computers have) is going to get to universal compatibility- each dive computer has its own data structures and requires drivers. And it would be pretty limiting. A converter is necessary because so few computers nowadays have serial ports. If there is an inexpensive universal interface now it's USB.
Which does not excuse the $90 cable. We designed the Cobalt to interface with an off the shelf USB cable- Atomic includes one, but if you lose it you can get another anywhere for a few dollars. That was a design decision made early on, and the added cost is trivial. We thought that the whole concept of having to pay extra for download capability would not fly in today's market. And like ReefNet, we have cooperated with open source and independent developers of dive log software and drivers. There is no reason others could not do the same. It would add value to their products.
Any way that is universal using off the shelf supplies would be fine IMO. I paid $5 for the last USB-serial converter I bought, a bit cheaper than $90. How much would it have cost to make that already there serial interface work with any regular serial port, or via USB-serial converter. I definitely think that USB is the future, and the cables are cheap and everywhere.
I think that it's great that with the Cobalt it uses a standard cable that you can buy anywhere for a reasonable price, and can be interfaced with by third parties. It is unfortunate that I will probably never own a $1200 dive computer, though it should be included at every level, not just the top end.