I actually take longsword lessons at the Royal armouries here in England.
Not all of the weapons we use look alike but they are all longswords - usually called bastard swords or hand and a halfs.
They dont all look alike as their development needs changed from 1350 to around 1530, this was because of plate armour advancement from the more common ( At the time ) chain mail and coat of plates.
http://images.google.co.uk/images?hl=en&q=coat+of+plates&gbv=2In early longswords you will see they are thinner as armour was less technically advanced then and there was no need for thicker heavier blades, it was also a good way to keep the weight of a weapon down. The advancement of plate armour caused swords to be developed in a newer fashion and you will find that later period longswords took on what is known as a riser ( the ridge down the middle ) which gives the blade a diamond cross section and improves structural integrity. This keeps the blade strong when thrusting into an opponents armour as many other blades would fail in battle.
You will also notice that nearer the hilt the blade will sometimes become thicker and wider then taper towards the foible or "tip", this is to push apart the plates of armour during a thrust.
In modern usage, "broadsword" inappropriately refers to a category of swords, specifically those whose blade geometry is designed for cutting and slashing attacks, as opposed to the fencing weapons and their emphasis on thrusts and stabs.
This began after the advent of the slimmer-bladed rapier, smallsword and epee during the Renaissance, and was picked up by museum curators during the 19th century as a catch-all for all slashing swords, including the Medieval arming sword,
longsword and greatsword.
So technically the picture showing Alucard swinging the sword IS a longsword as it comes under the broadsword category of today's historians. you can clearly see he has room for at least another half hand if need be.