Good eye Cirquerider.
Because the felt gets saturated and is malleable, it seems to slow down evaporation of the liquid wax, assists with pushing and delivering the wax into the bases better, versus a topical applicator like a cork or squeegee, etc.
The cork method, however, probably isn't far behind and does provide friction heat with enough elbow grease.....and of course there is the additional ironing option for optimal durability which will exceed that of hot waxing solids.
The liquid rub ons have a thicker sponge than the felt and basically works similar to the felt applicators. These are refillable and are a good option for applying bulk liquids as are our refillable sprayers (separate then the spray canisters). Note not all spray products have a felt applicator and a felt 'cork' or two are always a good item to include in your wax and tuning kits.
(I forgot to mention previously, if any odd behavior or bad links are found on the Interactive Wax Thermometer, please let me know. Additionally, a future project is to also convert the Racing Wax Chart into an interactive one.)
Here's last years Maplus Wax Test