in place, files could be verified. However, in GpgEx we provide a right-click solution for checksums. It could be interesting to add the mentioned checksum calculators to the option-list.
Just to be clear I think this issue is valid and we should add more checksum tools in the future. But I would want them to use libgcrypt and confirm to the standard *sum command line arguments like -c.
Note that there is no standard for this. In particular the encoding of filenames with special characters are different in almost all implementations. I tried to find a common ground for our implementation.
By standard I mean "behaves" somewhat like coreutils. Filename encoding,.. meh I see that this could be a problem.
I'd like to work on this, some gcrypt stuff would be interesting and with the gpg4win-tools repo I have a nice place for the tools.