Just like any design, the document provides recommendation on OSPF features. You must understand those features and apply them if needed. Not every design needs to be identical as there are a lot of variables thrown into each design. If you follow the design Best Practice from the document you've pointed out, you should be ok but also listen to the customer's concern - this is what makes you successful. If the WAN links are fast and reliable, then you can apply the same features as you would apply in the LAN.
HTH,
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Edison.