Well idk, I was about to sign into the app on my phone and uplaod the same pic directly to the site, eliminating picasa. I think that like apple, picasa must have its own server dedicated to the media files and maintaining the quality, as well as synching to all devices etc. But when your sending the picture over an inferrior network that limits whats being put through it does degrade the quality. Thats called packet loss isnt it?
For best picture uploads Ide put it all on Picasa and do it from there. It is a hastle, but you will get the quality your looking for.
Until the network can support the full capabilities of the GS5 there will be many issues like this. The phone can handle up to like 60mbps but my WIND network peaks at like 28.something. The phone is great, but it is difficult to take full advantage of.
Hope that makes some sense
EDIT:
Picasa is actually kinda cool to have. Auto uploads and ya can sit down and view them all in an organized fasion via browser or the Picasa program itself. Maintains the quality wherever you sign into view it until it gets sent somewhere 3rd party via a wireless connection. Give a try let me know what you think!