You haven't said what you mean by a 'Straight scene', so I'm assuming you mean a sex scene.
I heard someone describe a lot of the stories at Nifty as 'text-porn', and if you look at it from that context, I'm no more interested in reading a straight-sex scene than I would in watching straight porn.
On the other hand, I'm very happy to read stories about relationships, regardless of whether they are are gay or straight. So, a 'straight scene' that showed the love of two people, who just happened to be of opposite sexes, is something that I have no problems reading.
So, the answer depends on what it is you think you're reading. If you are reading gay 'text-porn', then a straight sex-scene is inappropriate. If you are reading a romance where the lead couple happen to be gay, then I don't think a straight romance in the same story is out of place. I personally tend to skip sex-scenes anyway, so it doesn't bother me if they are straight or gay. Love scenes, on the other hand, I'm quite happy to read, regardless of the sexes involved -- I'm reading for the emotion, not the mechanics.