The argument would be that regardless of what security you put on the wireless, you still don't have the physical security - i.e. someone doesn't need to walk into your building to use your network.
Beyond that if you're using strong auth/enc you can currently be considered safe, we have customers using that direct into their LANs (but then, we also have customers with WEP direct into their LANs!)...
If you are concerned or really need belt 'n' braces security, then go down the firewall/IDS route - there's no harm in it if you have the money. It really depends how much functionality and ease of use you need to balance against it.
Aaron
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Aaron
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