I can't share the opinion of Shareaza being leeching the Gnutella network. First, leecher do exist, that's no secret, but leechers are far less a problem that for example people that don't configure their firewall or router properly. I think firewalled clients are a much bigger problem.

Shareaza cannot leech Gnutella more than G2, because the upload queues in Shareaza are not configurable to differ between Gnutella or G2 uploads. They're both HTTP transfers, which are treated in the exact same way. However, the user may choose to disable Gnutella and to forbid (which doesn't happen by default) any upload to not connected networks, in this case Gnutella. But then it won't download from Gnutella either. Unfortunately, such clients may still appear in Gnutella's alternate source mesh, and get into the list of sources of a Gnutella client. This fools people into thinking that Shareaza doesn't want to upload to them, thus is leeching. But this is not true, it only disallows uploads, because Gnutella has been disabled on that client.

Shareaza clients can be downloaded from without problems, but it happens that people don't properly configure their firewall or router, which may make it impossible for Gnutella users to download from those clients. A push request is required for this and if the user doesn't have Gnutella enabled, then this push request will only be possible over G2.

Also it's worth mentioning that many people don't use all of Shareaza's network at the same time. Many people (including me) use it exclusively with G2.

Last but not least, it's unfortunately true that Shareaza's support for Gnutella is outdated. This is being worked on.