The angular distribution of the x-rays is basically uniform as you indicated, but there are beam restriction devices in use that aren't usually shown in a diagram, as in the typical diagram below.
Here is a more detailed drawing showing the isotropic radiation and a beam restricting device, which is less fancy that it sounds. Perhaps there are other fancier types.
The angled anode target are only angled around 10 degrees (6 to 15 degrees is what the source below tells me). The 45 degrees one often sees in diagrams must be an exaggeration. The angling helps with both heat dissipation and having a selected beam of x-rays be produced from a relatively large surface area on the target. The diagram below shows this better than I can explain it.
More information (and my source): http://en.wikibooks.org/wiki/Basic_Physics_of_Digital_Radiography/The_Source