Unneeded ministers?

There's much talk from ex-ministers (Chris Mullin and Digy Jones spring to mind) about how we have far too many ministers. A recent trend towards not filling vacancies seems to confirm that some posts can be left perfectly well unfilled.

When Lord (Digby) Jones stood down from Government it took some time, months, for his successor as Trade minister, Lord (Mervyn) Davies to be appointed. Maybe this is an exceptional post as, right from the start with the appointment of Lord (David) Simon of BP to the same post, Labour have been keen on getting senior businessmen to take this particular post.

But when Sarah McCarthy-Fry left the Department of Communities and Local Government to replace Kitty Usher at the Treasury, just a few days after the last reshuffle, she wasn't replaced at the DCLG. At all.

Did the work of the DCLG need 6 ministers (2 shared with other departments) as it did on June 9th, or 5 ministers (again, 2 shared with other departments) as it has from June 17th?

In a few weeks time, Lord Malloch-Brown will stand down from his post at the Foreign Office - for reasons that don't stack up his long-standing decision to stand down could only be executed 7 weeks after a major government reshuffle that saw most of the other Foreign Office ministers change.

Will he be replaced immediately, or this be another example of a post that doesn't need filling?