First, Apple is only using Netscape's portal services right now because their contract with Excite expired, and Apple didn't want to continue partnering with a company that might not be around in 3 months.
Second, Internet Explorer is Apple's default browser because of the agreement Apple reached with MS back in 97, that went as follows. MS would continue to develop Office for 5 more years, in exchange for Apple 1) dropping their lawsuit against them, 2) making IE the default browser for that 5 year period, and 3) MS buying $150 million of non voting Apple stock (this being mainly just a vote of confidence in Apple for the street). Come mid 2002, this agreement will be expired.
So Apple has either to renegotiate with Microsoft, continue on with the status quo. My guess is now that the DOJ is off of Microsoft's back and they eseentially own the browser market, Apple has very little bargaining room. I don't think Microsoft would dump Office for the Mac - after all, it is very profitable for them, and it does keep the DOJ somewhat at arms length. Surely killing Office for Mac would create a new rallying cry of "Monopoly" from many MS detractors, and could possibly force MS back in to court, proving costly.
Apple will probably keep IE as their default browser, unless it falls far behind the other choices for the Mac.
Omniweb is very much a wild card. OW 4.1 is a MAJOR improvement over 4.0, and will be seen by many as a very good replacement for IE. If the Omnigroup can deliver on their intentions, OW 5.0 will be the only browser you will ever need for OS X. However that could be as much as a year away. I think Apple's major concern is that IE for Mac is starting to lag behind what's available on Windows. In 2000 when IE 5 debuted, it was way better than the Windows version. Now in 2002, it's still more advanced feature wise than the Windows version, but performance wise it still feels like it's in beta. Maybe MS is working on IE 5.5 or 6.0, and didn't want to devote too many resources to getting the first carbonized version out. Only time will tell...