And I didn't say a stronger candidate was necessarily more conservative. Note that many of the candidates in trouble---or, perceived to be in trouble---are liberal, many are conservative. It depends on the district.
It's just that the whole perspective of the WaPo is never that "Republicans could be even stronger" but always Dems "lost" the seat, never Republicans "won" it.
Reporters write to the prevailing script which is can the Democrats win back the house. That is the story line. It isnt how do the individual races stack up, its what are the Dems chances of finally getting out of the wilderness.
For information on these races you might want to check Elections and Campaigns. The guy there handicaps each race giving a percentage probablility for winning. These are updated frequently. You can find it here http://www.campaignline.com/oddsmaker/
You might also google Barone, Cook, and Orinstein. All of them have had articles on House races published on Real Clear Politics during the past week or two.