Another good article. Well done.
Readers might want to note that the spatial reference identifier not only refers to projected spatial reference systems as suggested, but to geodetic spatial reference systems too (i.e. ones based on lat/long coordinates).
In fact, the sys.spatial_reference_systems table is *only* used for non-projected spatial reference systems, since these are required to apply the relevant model of curvature to the earth when using the geography datatype.
When using a projected system based on the geometry datatype, it doesn't matter what SRID is supplied - the results obtained of any methods will be the same.
For any readers wanting a further introduction to different spatial reference systems, and their signficance to the geometry and geography datatype, try:
"Beginning Spatial with SQL Server 2008" (Apress)