Product to Product Compatibility

We have a product that is tightly integrated with MS Office (Excel in particular). The vendor of this product stated that it will take 3-4 months to provide a compatible version of the product after the new MS Office (XP) is released.

Question: Is this lag in release time reasonable? What is a reasonable time for a vendor to provide a compatible product? With an OS release, I would hope all major vendors would be ready on or near release date, but does/should this same requirement apply to integrated products?

Said another way, are the compatibility expections the same for the Product to Product relationship as they are to the OS to Product releationship?

Any comments would be appreciated.