I feel that there are multiple issues at hand:
Firstly, I don't believe that we should blindly follow everything that is followed at Stackoverflow. The nature of the community at SO & GIS.SE is very different, and so is the subject matter. There are many libraries & applications that do the same thing in General programming and Web development; In my experience, this isn't strictly true in the case of GIS. The output might be same, but there is a large spread, when you consider the process, ease of use, platform and Cost. Another reason to not be so pedantic, is that we have far fewer questions posted each day, and answering such questions is still manageable.
Secondly, we need to define what exactly is Meant by 'shopping question'. If the Question is 'What can I use to do X?' I feel that we should close it. Not because it is a shopping question, but because it shows that the OP has done no research.
If the question is: 'What are the advantages and disadvantages of various applications/Libraries that do X?', I feel that it is a good question. While some people might post a small, one line answer, the most highly voted answers tend to have a lot of information, which is the extract of the poster's experience and knowledge, and can serve as a wonderful storehouse of knowledge for users. The following Questions lie in this Category:
There is another class of related, Highly-voted Questions, that I have a problem with. These are basically just asking for a list of options. I feel that, though these posts have valuable information, and open your eyes to what is possible, they don't belong on GIS.SE. The following questions lie in this category:
In my opinion, just enumerating the elements of a list is not useful. What would be useful is if more information is present in each answer, detailing the advantages (& disadvantages) of that option over others.
I remember that stackoverflow had locked and preserved such posts, for historical reasons, instead of closing and deleting them. Maybe the Mods could look into doing so, for these highly voted old questions.