Yes, travelers from countries that require a visa to enter Laos must pay the visa fees regardless of whether they arrive by bus or by air. The entry rules and visa fees are consistent across both land borders and airports. Some nationalities, such as Filipinos, may receive a free 30-day stamp upon entry.
I'm from one of those countries. Slight digression of possible interest to those travelling a lot: The officer stamping me into Laos was friendly and chatty (slow day.) And so I asked how many times I'd be allowed in Laos in, say, one year. He talked a bit with a colleague and then replied "3 or 4".