[raldi]

"Non-engineering company" -- ha!

But to answer your question: Mike Bloomberg's autobiography talks about this. When they started in the 80's there wasn't as much great off-the-shelf software as there is today.

Their customers were (and always have been) insanely demanding when it comes to reliability and speed. The last thing Mike wanted to do was be caught sheepishly explaining to the CIO of Merrill Lynch, "Well, gee, our Oracle database has this bug they can't fix for the next two weeks..." or even "...this optimization they can't make for the next six months"

This is a company that invented its own layer-2 network protocols 35 years ago just to squeeze every last drop of performance and reliability out of the hardware. Of course they wrote their own database (actually two -- there was a comdb 1 of of course, too)