There are a few other issues though. First, the only reach weapons with +3 prof are non-blades, and each weapon group has associated feats and magic weapon types. Axes are probably the best example, as it gives you high crit property. The increased push ability for spears can come into effect, etc.
Either way, it's something that may not be a big deal as a houserule, but it does seem like part of the reasoning isn't just flavor. One note ... your only choice of heavy thrown weapon you initially have proficiency in is the javelin ... while axe/hammer prof would let you have. You are a bit better than the average defender, but you still have little in the way of ranged attack power, so it would come up. Just making sure people keep in mind all the points if they choose to go the route.
The biggest unintentional issue might be in magic items. You still have the properties when an item is used as an implement, so there may be powers you can't get on a blade that have quirky interactions with swordmage implement powers.