They do limit the quality of images. If you want to see the highest resolution image, take any of the image urls and replace 'web-<WHATEVER>' with 'web-original'.

This is a small step in showing they are trying to understand what it means to 'open up' access. Note that museum policy does not necessarily agree with the law. In fact US law protected the user in cases where museum policy restricted use.

The #1 cited fear within the museum for restricting access to imagery of things like public domain objects? "We don't want people selling shower curtains with our art on it".

The more people make interesting use of the content, the stronger our case can be. Our being the people working for the museum who want to share more data.