At Linden Lab, our intent is to enable the development of third party viewers and the improvement of our own viewer through mutual sharing of the requisite common technology. We think that LGPL is a better license to accomplish that sharing. Even though it was originally written to apply only to libraries, there is significant room for interpretation when using it.
Our interpretation is this: modifying the build procedures provided in the source code to produce a library containing a subset of the licensed code is a minor programming exercise. The result of linking that library (which may be either a static library or a shared one, and either is allowed) with whatever other code is used to build a viewer is again a minor problem. The results are essentially indistinguishable from those in which the developer just modified the build procedures in place to produce an executable application. Essentially, the details of the linkage procedures used are a matter of packaging and have no end user effect. In practical programming terms, a library is just a convenient package - the requirement in the LGPL is like requiring that a grocery store sell a product only if it is first placed into a shopping cart while inside the store. Essentially a library is just that - a shopping cart full of individually compiled modules, so there's no real difference between using a library and just using the modules separately (one could build a library containing exactly one module, or build an application that had only one module and one library).
It is our intent that developers be able to use the components that we have licensed under the LGPL to produce viewer applications, regardless of the linkage procedures used, so long as they make available any changes to those components as specified in the license.