I obviously can't speak to what is on the SF web site, but I can let you know how I use factory methods.
Typically I use them in one of two situations:
- There are bunch of ways that an object can be created and constructor overloads are either confusing or don't work (because the arguments wouldn't be unique). In this case it is much easier to create shared (static) factory methods that have clear names and precise arguments. I use it a lot with Forms. I.e. I have a form that can be opened with a single record, or in data entry mode, or with all records that match some criterion and the current record being specified. I could have constructors something like:
public MyForm() {}
public MyForm(int id) {...}
public MyForm(bool dataEntry) {...}
public MyForm(int parentID, int id) {...}
But this is confusing and I have trouble remembering all the permutations. So, instead I would create a set of factory methods:
public static MyForm CreateSingleEdit(int id) {...}
public static MyForm CreateDataEntry() {...}
public static MyForm CreateParentEdit(int parentID, int idToNav) {...}
Now I have no limitation on how complex the constructor is and I have help remembering how I have setup a class.
Hope that provides a bit of clarity. I'm sure others have more/better examples, but I thought I'd get the ball rolling! 