"Was this creator developed as an internal Shapeways tool by smart Shapeways employees or with third party tools and assistance (like Mixee Labs)? "
We wrote it using our open source AbFab3D toolkit. You can download that at AbFab3D.com That said it is a programmers toolkit so you'd need to be familiar with Java to use it.
"On an unrelated note this creator seems rather limited because of discrete ring size steps and length limitations. Why not allow an option to enter numerical values for diameters, allow smaller diameters, and extend the length control to at least several inches? For example it could also be used to generate anything from small custom beads to larger custom containers like cigar tubes."
I more favor an approach that puts out a bracelet creator, a bead creator etc. Ie small variants of this core creator. This way you can put inspiring product photography next to them and add custom options as desired. Ie a bracelet creator might want to add clasps where as ring creator doesn't need that.
If more people start asking for the bracelet creator then I suspect we'll find the time to do it. Or we've released the code so others could take it modify it for their own creators.
The x3db format is not as widely adopted as I'd hoped(I wrote a good chunk of that specification). I know that Netfabb reads it so maybe you could use it to write back to stl. I run another project called Xj3D that can be used to convert them. But sadly it's also a programmers library so its not very user friendly.