The only valid reason for people to use C# for the accounting system is they are not business centric application, they do not need the convenient of VB.Net in business application, and they may be very used to C# programming for another system base program...

Having said that, C# accounting is not very different from VB.Net Accounting, they all share the same components and architecture, and in business environment, many advanced C# structure does not apply. I would only recommend C# source code for accounting software when the developer are C# in nature, if you are from Visual Basic 6 or other languages, and you are developing business application, never use C#!

VB.Net is easier to learn, master and most business application are developed with Visual Basic and VB.Net! You can easily find many visual basic and vb.net based application, this make the development and resources better!

Certainly, on dot net platform, every compiled component written in dot net language are interoperable, there are no barriers between them, but if you can consistently use the same language, it makes thing even more easier.