Those URLs are internally rewrote to default.aspx. So they are being rewritten/forwarded to default.aspx, instead of news.aspx. The BE default.aspx page (your news.aspx) is what handles displaying posts by category, posts by author and posts
by tag. Looking at the code now, default.aspx is hard-coded in there.
The only option would be to modify the BE code source code, and recompile the BE core project to produce a new BlogEngine.Core.dll file -- which goes in the /bin directory.
In the BE core project is a folder named /Web/HttpModules. In there is a file named UrlRewrite.cs. In there, if you search for "default" you'll find about 10 or so references. Those instances of "default" should be renamed
to "news" -- so they are rewrote to news.aspx instead of default.aspx.
Making tags work will probably depend on where the link is coming from ... so there might be 2 or 3 places that need to be updated. One is in the /widgets/TagCloud folder (widget.ascx.cs). Another is in the BE core -- /Web/Controls/PostViewBase.cs.
In there is "TagLinks" where the tag URLs are constructed. For these instances, the links are being constructed like /?tag=tagName ... and should probably be changed to /news.aspx?tag=tagName.