The actual numbers that go to make up these images are needed to do any science with them - only a fool would try to do science with a JPEG image, but this does happen. The 'scientific rights' refer to the use of the raw numbers for these images in scientific papers. These rights apply for about 1 year after the observations are taken so that the team that has spent years building the instrument and sorting out its science can benefit. This data then becomes completely public.

In these images you're largely seeing thermal emission from dust at temperatures of about 20-50K. The wavebands chosen cover the peak of the black body spectrum at these temperatures so we can get an accurate measure of how warm of cold the dust is.

The poles of the scan are actually the ecliptic poles, perpendicular to the plane of the planets within the solar system. This is set by the fact that Planck rotates with it's bottom pointing towards the line that joins the earth and the sun from it's position at the second Lagrange point. This ensures that earth and sunlight never impinge on it's sensitive detectors and helps to keep the whole instrument as cold as possible. The scan geometry is thus quite tightly restricted by these requirements and, as you say, the deepest fields will be at the ecliptic poles.

We actually don't want to study the centre of the galaxy with Planck as the galaxy is the major foreground contaminant to the CMB data. Fortunately the eclptic poles aren't aligned wiht the centre of the galaxy.