There are almost always one or two teams, in any given season, that go on a blinding run and impress everyone. Last season it was Swansea and West Brom. You have to say in their case it was mostly (though not entirely) down to individual players (Michu & Lukaku respectively).
We are that team this season, but we have done it as a team. Our big expensive signings have given us something but have not been the headline-grabbing successes we might have expected (i.e. Lovren and to some degree Wanyama have done well, but nobody outside of Southampton is talking about them).
Point is, of course I want to hold onto our players, and I relaly want us buy some more good ones (especialy in certain areas). Nonetheless, we have a good team with a good supply of youngsters who the management are happy to trust and promote, and if things carry on like that we have a chance of not doing what Swansea and West Brom have done...
If we sell Shaw, we have others to come in - it won't be the end of the world - though I genuinely think it would do both him and us good to hold onto him for a couple more years.