Actually it isn't. Point/prim/edge numbers are volatile, most SOPs that create geometry won't group the newly created output, extrudes and bevels won't deal with UVs, Sops that create primitives do-so with near degenerate faces, procedurally selecting loops is a pain, procedually splitting and knitting is very difficult, many SOP operations require manual cleanup... list goes on.
For destructive modeling in the viewport SOPs are pretty good however, once your muscle-memory sets-in. Definitely lacks many of the comfort features of other programs though... its just hasn't received enough attention from top modelers, who avoid it because its been neglected...