I can't vouch for whether the point made in the article is in fact true, but it does highlight a central fact about campaigns for the presidency. They are won by whoever is able to both retain their base and lure a majority of the swing voters.
The term "the base" refers to the hard core party identifiers, many of whom are members of the tea party movement. They tend to hold extreme ideological positions on issues and are resistant to compromise. The term "swing voter" refers to the small group of independents that can switch their votes from party to party based on the unique circumstances presented in each election.
We spend time when we discuss elections and parties discussing these terms more fully - as well as the issues associated with each (example: is there such a thing as a truly independent voter?) - but for now its useful to think of each party's convention as their effort to both solidify support by the party base while reaching out to the middle.
The problem is, what excites the base may drive away the center, and what interests the center may repel the base. The article linked to above argues that Romney's effort to reach out to the middle, may cause the Tea Party folks to sit this election out. They may see actually it more beneficial to wait until 2016 to support a candidate they find more appealing than Romney.
It's just a hunch though - but not a bad one.
