This is a mistake, these models are not being phased out.  They can be found by going into the Large Enterprise area of www.dell.com.  > Go to www.dell.com, > click "For Large Enterprise" > click "Servers, Storage, Networking" > click "Networking" You are right, these used to be included also in the Medium business area, and they probably still need to be.
The website currently no longer lists the 5500, 6200, 7000 or 8100 series PowerConnect switches in the Small/Medium Business networking section. Searching for a 5548 shows no products. All that is listed is the 2800, 3500 and Force10 product lines. Is this just a website error or are these models being discontinued/replaced?
PowerConnect switch model changes?