For their time, the BS1 and BS2 were considered pretty open, powerful, and cheap compared to the other options out there (PICs with expensive programmers and steep learning curves, etc.). Being able to drive a 44780 LCD, read a rotary encoder, and do basic serial I/O in the same hobbyist project were well out of the grasp of the common hobbyist in the late 90's, but the BS2 made all those things possible for $50.

Arduino hasn't really set the bar that high, it's the next/current evolution of something that has been going on ever since the commercialization of the first NP junction.

Like the Stamps before it, the Arduino is a neat prototyping device, but not something you can build a 'product' around with any great scale beyond a hobbyist market. The biggest difference in that in its heyday the Stamp didn't have the full power of the Internet to make people aware of them. You mostly had usenet or publications like Nuts N Volts to expose people to the possibilities of simple micros. The Arduino has gotten great exposure because of the Internet, but in the grand scheme of things hasn't really done all THAT much. The article on Make references 100000-150000 Arduinos sold. Maxim has given away more PICs than that as free samples.

Sure, the Arduino is neat and cool, but the fawning over it you see on sites like Make heavily skews reality. 30 years ago if we had the Internet this blog post would have been "Why the 555 won and why it's here to stay"