The combination of Grindstone and Painter's Servant means that once Grindstone is activated, you can "deck" a player in one shot., since every card in a player's deck will be the same color (yes, even lands). This makes it a rather nasty win condition. The only way to stop an effect like this once it resolves is to play a card that would shuffle itself and that player's entire graveyard back into their deck (like one of the major Eldrazi such as Emrakul). Barring that sort of shuffle effect, Grindstone/Painter's Servant is a viable strategy that has been a profitable deck for many Magic players over the years.
The Imperial Painter deck is much more popular online due to the fact that its overall cost is so much less. Imperial Recruiter is a $200 card in paper due to its rarity from being only printed in Portal Three Kingdoms. As the Recruiter was a rare in the widely drafted Master's Edition II set on Magic Online, copies are only about $13 a piece.. Painter's Servants are also about 1/5th of their paper price (roughly $2 vs $9). Grindstone isn't exactly expensive, though, only about $8-9 online vs $15 or so in paper.
But with the Tempest Remastered reprint on the horizon, there will soon be some more supply of Grindstone. It is being reprinted at mythic rare, however, so it will not be opened as nearly as much were it still printed at rare. This rarity decision was based on its power level in the draft format, as any "mill" cards like this are powerful in limited formats. In any case, there will be new copies on the market which should lower the acquisition card of this powerful Legacy card considerably