I think that simplicity of their product line drives some of the corporate sales as well. If I tell some random IT department to get a macbook, there is only so bad of a machine they will pick for me. HP, Lenovo, and Dell have some really shoddy machines at their cheap end. At a startup you can specify exactly what model you get, but when it's a large IT department saying "generic windows machine" is much more of a risk than asking for "a mac".