Do All Wine Bottles Need to be Laid on Their Sides?

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Do All Wine Bottles Need to be Laid on Their Sides?

From:
http://www.epicurious.com/articlesguides/blogs/editor/natalie_maclean/index.html

OK, this question has been bugging me for a bit, and I'd like your help. I know that bottles sealed with natural cork should be stored on their sides to keep the corks moist so that they don't dry out and let oxygen in, which can harm the wine. Conversely, bottles sealed with screwcaps, glass closures, beer caps and plastic corks don't need to be on their sides because these closures don't expand or contract with moisture.

However, I'm puzzled by sparkling and fortified wines. Bubblies, usually sealed with a large natural cork, have tremendous pressure inside the bottle due to the trapped carbon dioxide. I've heard that this is why these bottles don't need to be stored on their sides, but is that correct?

Fortified wines, such as sherry and port, have higher levels of ...

... alcohol and often higher levels of sweetness. Both are preservatives, so does that mean it's not that important to store them on their sides?

I'd love to know some of the science behind this. It would be great if we could safely store some bottles upright as this can often be convenient or space-saving.

Hope to hear from someone on this.