I think videogame music, in it's early days, had no choice but to be very strongly melodic due to the limitations of the hardware. When you only have four channels to work with, you can't create a deep moody orchestral athmosphere -- your only choice is to write a strong, catchy melody.
I think these technical limitations forced a great deal of creativity on the part of the composers. This effect has lessened with more recent generations of consoles, but I think there is still somewhat of a lingering effect.
And songs with strong melodies tend to make for great remixing.
I also like the way videogame music separates genres from the cultures typically associated with them. For example, let's look at popular music. Being a pop star (especially a female one) isn't about writing good music, it's about being a sex symbol. Being a hip-hop star isn't about writing good music, it's about being a badass gangsta. Being a country star isn't about writing good music, it's about being a redneck. The same is true to varying extents with just about any genre -- electronic, metal, classical, you name it.
The VGM scene really separates the genres from those cultures, though. You can be a nerdy white guy and write rap. You can be a 20-something japanese guy and write irish folk. You can blend genres and write in any style you choose and nobody will so much as raise an eyebrow. I think the VGM scene is great in that it allows artists to be judged solely on the merits of their music, more so than just about any other genre of which I'm aware.
See above -- VGM's biggest strength is that it does not confine artists to a particular style. It's biggest strength is how eclectic it is.
*shrug* it's hard to make a blanket statement here that holds true across the board. It's the music I grew up with, it's the music that got me into music, it's the music that I've always loved.