Reviving an old thread, but I have some thoughts...
Unless you live in a totally high magic world, what respectable, non-arcane scholar is going to trust in the divinations of some strange wizard? Why have locksmiths when you have the spell Arcane Lock? Why invent breathing apparatus to explore under the sea when you've got Alter Self and Waterbreathing? Better yet, why sail across the ocean and discover the 'new world' when several scholars can prove the world is round right there at home? Why go to the moon?
There are several reasons why non-magical archaeologists, historians and tomb-raiders would have a place in a D&D world.
Wizards like to keep knowledge for themselves. Sure, it takes some intelligence to learn magic but by the rules anyone with an 11 Int should be able to fire off a magic missile. They keep secrets to themselves or within their own societies. Are they any more likely to share the secrets of a lost civilization than they are to share the secrets of magic?
Wizards are focused in their interests and research. An archaeologist wizard might be very interested in knowing about the magical beliefs or rituals of a lost civilization. He devotes his entire life to learning magic. Is he going to devote as much attention to things that might interest a true historical scholar, such as ancient methods of grain storage or the etiquette of the high court? Does a 20th level wizard want to spend time using his hard-earned magic learning about the day in the life of the hairdresser of the concubine of a long-dead Emperor? A truly devoted archaeologist or historical scholar might, but a wizard?
Some traditional scholars might not trust the "research" of a wizard, a casual spell fired off here or there. In addition, while a spell might give some information, nuances or context of information might not be readily noticable through a spell.
Unless everyone has some magical talent in the world, the ability to provide proof and teach others about discoveries is going to be sorely limited if all proof is provided by magic. "We'd love to explain exactly how we know that the tablet is 3,000 years old, but you would have to be a 12th level wizard with access to these spells to understand." That's not going to go over well among other scholars and students.
Political backlash. If wizards are the ultimate authority on history and past events, this gives them a certain power that others might not appreciate. Look at it a certain way, and Copernicus wasn't just condemned for his discoveries, but because the church and church-supported monarchies could not justify their positions if his claims were true. Add magic into the mix. A political or religious figure can dispute a thesis for a time, but a thesis backed up by high-level spells? They are more likely to fund or support an expedition by (fallible) traditional scholars than anything done through magic alone. There's also the uncomfortable possibility that a magician might contradict the powers that be or uncover some 'dirty little secret', which would be much easier to hide from a normal academic or treasure hunter.
I could go on for a while, especially with magic-user stereotypes and preconceptions. Suffice it to say that a discovery means nothing if you cannot share the discovery with the common man or pass the information along in a format that is readily understood. If you can't explain how you arrived at the solution, the equation is meaningless. Not everyone has magic (arcane or divine, although I use wizards exclusively in my examples). Common (non-magical) people are going to want to rely on common, non-magical thought and reasoning. Tangible evidence and work that they can relate to and follow along with rather than a wizard coming out of a tomb and saying 'King Whatisname's ghost told me that he died alone choking on a pretzel 3,000 years ago through a divination spell I cast." Where's the proof? Somewhere along the line, someone is going to want to find the fossilized piece of crunchy snack pastry lodged in his throat and find some historical records of such an event. Otherwise it's just some goofy wizard in a pointy hat making a bunch of claims the average scholar can't back up.
