Hmm... Does it matter?
It seems backward to me to say "Well, there is no software written in C to tackle this problem..."
Under what circumstances would a customer care whether a solution is written in Java or not?
I tend to agree with gmagana that in this context most customers wouldn't care whether it's Java, C, PHP or PL/1. However to say that customers don't care about the language/platform in all circumstances isn't strictly true.
I previously worked on enterprise software for the financial markets, where a segment of the market is split into sell-side (investment banks, etc) and buy-side (typically investors of other people's money).
<SweepingGeneralisation> The sell-side is very pro-Java (especially the US market) and often anti-.NET as they have a lot of in-house expertise in specific technologies. </SweepingGeneralisation> As we had a .NET/C# product, it was easier for us to compete on the buy-side than on the sell-side.
Bottom line - it depends on the nature of your customers whether they care about the platform you use.
In answer to your specific question, I would suggest the absence of a Java solution indicates that it is easier to build web apps using other technologies. (Not sure what you meant by "forum/community software", but Atlassian 's products are built in Java and they have offerings in this price range).
Java's roots are in enterprise software. It is tuned to the needs of enterprises such as reliability, performance, scalability, et cetera. Enterprise software is expensive, and is sold by sales people from big companies (e.g. IBM, Oracle, SAP) getting big commissions. It is often sold to run on big expensive specialized servers. This makes it hard to price Java products in the hundreds of dollars.
Software written in PHP, Python, and Ruby tend to come from small companies on small/shoestring budgets and are designed to work on cheap servers. (This is a generalization only). Sales are direct, and often don't involve sales people (with commissions). Software people make their living on installation, customization, and consulting.