Personal milestones and achievements in MMOs is moving in the direction of achieve your own way. If you want to pay cash to buy shiny bauble #42, go ahead. If you want to grind mobs for a week straight to buy shiny bauble #42, go for it.
The one thing that hasn't caught up with that direction is outside player perception of achievement. Those that grind for the bauble will think the cash player is a lazy spendthrift. The cash player will think the grinders are daft for spending so much time in game.
It's just another aspect to add to the traditional PVE vs PVP, casual vs hardcore, and RP vs non-RP arguments.