A memo from Rick Davis of the McCain campaign states:
Until John McCain secures 1,191 delegates, we must campaign aggressively for the Republican nomination, and that requires additional resources in some of the most populous states in the country. We cannot turn our attention to the Democrats and their enormous war chests until this nomination is secure, and we cannot accomplish that goal without your additional help.
Okay, so, this is a fundraising letter - but I do think there is a misconception here, in my opinion.
That is - there's no reason McCain can't run against the Democrats and for the nomination at the same time.
It is true that Texas is a big state with a lot of delegates that McCain will win in November anyway, and so wouldn't need to spend much time there. But there's also some oppurtunities McCain can take advantage of while he's fighting to get the rest of the delegates he needs to make the nomination official.
For some of the states coming up, such as Vermont and Rhode Island, McCain is a pretty sure bet to win the nomination and yet it is unlikely, given recent trends, for the GOP to win there in November. On the other hand there are some places which McCain can build up enthusiasm for his nomination at the same time as he seeks out voters for the general.
This month, the next big state primary is Wisconsin. A few weeks later is Ohio. In these two cases we have states that McCain needs to appeal to not in order to win the nomination contest, but also because these are "swing" states. Considering trends in recent elections, in order for John McCain to win the Presidency he will need to win one or the other. Bush lost Wisconsin both in 2000 and 2004 by a margin of less than 0.5 %. Bush won Ohio both times by less than 4 %. Since Ohio is worth 20 electoral votes to Wisconsin's 10, Ohio is more crucial. Still, Wisconsin could prove vital as well, especially if Iowa or another state goes Democratic. And the fact that McCain has worked closely with Sen. Feingold may help swing independents. Ohio and Wisconsin are both real possibilities for McCain to win in November, but neither is a sure bet right now. It would make sense to take this opportunity to focus on these two states and reach out to general election voters while at the same time reaching out to the Republican base. Both independents and Republicans are able to vote in the primaries of Ohio and Wisconsin, and McCain will need the support of both groups in order to win in the general.