The 737-800 did not have winglets at EIS, in fact they were not certified until several years after the -800 entered service. I believe they are now baseline on all new production -800/-900 variations.
Retrofit of the winglets is pretty simple on the 737-800/-900 due to minimal structural modifications required. 737-700 requires significant structural changes hence retrofit is quite a bit more difficult and expensive.
The -700 BBJ uses the wing from the -800, and hence can take winglets with minimal structural mods.