Main problems with Smalltalk: it's not popular. Popularity results not so much from the quality of the product or idea, but from history and marketing. Marketing Visual Basic [the MOST successful language in terms of $$$] was done by a company with a big guaranteed revenue stream run a by a shrewed money-making management team.
Smalltalk was invented at Xerox in the early 1980's, but Xerox had no idea what to do with it commercially -- Xerox didn't market it or use it very much -- and then a few years later Xerox was being clobbered by Japanese copier companies and didn't have the money to market the hell out of development platform.
Consider what could have happened if PARC had been a Microsoft research facility -- if Bill Gates had commercialized Smalltalk instead of Visual Basic.
As to the other big development at PARC - windowing / easy to use interfaces - Apple took that idea and commercialized it, and then Microsoft copied Apple. Note that when Steve Jobs founded NEXT, Inc. he copied not only the idea of windowing interfaces, but also the idea of an OO application framework, having learned to look beyond the surface. NextStep [and now Apple's Cocoa] uses Objective C -- And Objective C is C with Smalltalk-like OO extensions.
If I remember right, Xerox Parc also developed ethernet (but didn't make money at it) and the predecessor of PostScript (but didn't make money at that).