I would hazard a guess and say that most test systems use LabVIEW as the development environment (with LabWindows as a subcategory). Why? I've programmed test stations in all three languages over the last 15 years (for testing, I first used C++ in 1994, VB v2 in 1996, and LV v4 in 1996), and I used to be a big fan of VB. Now I've used LV almost exclusively for the past 4 years.
Does it have to do with "getting there first?" Well, let's see. C++ has been around since 1985 (and regular C since 1972). Labview was created in 1986 for the Macintosh platform and was ported to Windows in 1992. Visual Basic was introduced in 1991. Looking at dates, either C++ or LV wins.
Is it because LV has a lot more language support? I don't think so...C++ has a worldwide user base, and Microsoft has historically had plenty of support for it's flagship programming language.
Is it because LV is focused more on testing? Maybe. C++ is a general-purpose language, which could be both a strength and weakness. VB was historically used a lot for DB interfacing and front end GUI apps. LV has it's diagram that looks like an electrical schematic, ready support for all kinds of test instruments, and National Instrument's (NI) claim that it is designed for "test, measurement, and control applications."
Personally, I think it has more to do with having a champion than anything else. C++, while created by one person, is a universally accepted standard language and lots of companies build compilers for it. Visual Basic is supported just by Microsoft, but I think they've always wanted it to be an alternative to C++ while at the same time promoting Windows as an OS.
But LabVIEW has always been about testing. NI has always claimed it is the perfect tool for test apps, they continually push building a community of users for it (free introduction seminars across the country, user groups in larger cities), and developing new test tools for it (motion control, DB tools, vision). Yes, LV is supported by a single company and if NI ever goes belly up a LOT of people are in trouble. But sometimes a single backer with deep pockets can help.
Comments on this are appreciated.