The problem has been discussed on the Steam Forums. The problem is that each game has to have a binary-identical version of the vc++ redistributables. Since games link against different versions of these libraries, steam always installs them the first time as a safeguard.
Credit to mordi2k for finding the post
Here's a link to the steam forum post about it. The text is quoted below.
FYI, running this is not a matter of making sure your overall DirectX
install being up-to-date. Microsoft has a helper library with D3D
called D3DX. You'll find binaries for this like d3dx9_43.dll in your
Windows\system32 folder. There are over 40 different versions of the
D3DX library for D3D9 alone, and many more for D3D10 and 11 as well.
Each game that uses the D3DX helper library is linked to a specific
version. As such the game must run the correct D3D installer version
that it was specifically compiled with to ensure the binaries exist.
Even if a later version of the binary is already installed, that
version cannot be used, and even if your DirectX install is up-to-date
because you've run a more recent version of the installer that is not
guaranteed to have installed all previous versions. Even worse, if a
version is installed for x86 it doesn't guarantee the same version is
installed for x64, so 64 bit and 32 bit games may need to run the same
exact installer version but targeting different platforms when run.
Furthermore, Microsoft's licensing terms prevent anyone from
distributing the files directly, the only way to distribute them is to
run the installer, that's also the only supported method from
Microsoft to check that the correct version installed. Trying to
manually check for the correct versions is extremely complicated
because there are numerous files that must all be present and
individual system configuration options like dll search paths
complicate the situation. In addition, the dependencies and required
checks may change in each new version of the D3DX runtime. The code to
check correctly and repair broken installs all exists in the installer
and running it is a guarantee that the correct binaries will exist
when you run the game and prevents lots of bad cases where a game
would fail to launch with an obscure error if a windows install was
either missing the correct version or somehow corrupted in the past.
Games which don't use the D3DX helpers (such as Source engine games)
don't require running the annoying installer on first launch as they
only depend on major d3d9/10/11 versions being installed. However,
games that do use D3DX must run it as it's the only way Microsoft has
allowed for distributing and checking the version info on the files.
So that's why we do it for lots of game installs. We can't stop, it's
required due to a bad versioning/packaging scheme as well as bad
redistribution licensing terms on the D3DX libraries.
The one thing that could be made better on our side is that Steam
could be smart enough to know if an exactly matching version of the dx
installer is already downloaded and share that content so you don't
download it with each game. Since the installer is relatively small
compared to most game installs that wouldn't be a huge win though and
requires a good deal of new complexity for partners in how they
package up their games and manage installation dependencies. You'd
also still end up with lots of different versions of the installer,
since as discussed above they are often targeting different D3DX
versions and as such are all required. As such any improvement to
avoid duplicates isn't an immediate priority, but we may be able to
improve it slightly in the future.