I have to agree with some. It's not always a problem.

I have used a 7x10 lathe for years and have no problems parting aluminum or steel. I use both a HSS blade and a carbide insert and the only times I worry about 'flex' is when I forget to tighten the gibs.

Yes, there are some tricks to make it work every time, but it seems that there will be some tricks to getting a vertical toolpost to work too, not the least of which is centering it, aligning it, and replacing it.

There are several good threads on the forum about parting, and by following the guildlines it's pretty painless.