Well, I just compared the two machines and I got the MacBook at $1598 with a nicer case (obviously subjective), faster bus speeds (20%) and a better graphics card (also about 20% by some benchmarks), as well as gigabit ethernet, but smaller HDD. The XPS M1330 came to $1403. So in the end you get a slightly better machine for slightly more money from Apple. More or less parity.

I'm not sure where you got the extra $200 on the Mac from, but the extra $200 I had on the XPS I'm assuming probably came from the little options like the LED backlight, and the better Windows License to get a closer match for features.

Nothing is going to be an exact match (unless someone does release something with exactly the same specs I guess) and largely someone's concept of value is going to vary by what is important to them. You may not care about the gigabit ethernet, or may consider the difference in bus speed or graphics capabilities largely irrelevant, but they do create a price difference. You may not care for the aluminium case or glass screen, but I'd expect that it costs a bit more to make, and I think they're worth it. I'd also rather have Mac OS X on a laptop than Windows, and that's worth something to me as well.

Looking at Apple's website, we could ditch the aluminium and glass, and the LED backlight to take about $350 off the price of the MacBook, only saving about $200 on the XPS, and they become almost the same price.

The problem with using a GPL compatible license is that anyone who modifies your code can return your code and its modification back under GPL, at which point no one else can use their modification together with the improvement. This is important for companies that have to interface their code with proprietary code that they cannot release, because if they release their code under a GPL compatible license it is almost certain the code will immediately end up being modified and rereleased under GPL, at which point they cannot use the modifications themselves. LGPL explicitly doesn't protect you from this to make it GPL compatible.

Basically, if you don't want to use GPL because you want some extra freedom, and you want to enforce that freedom as a right of people who use your code or derivatives, you must be GPL incompatible. If you don't want to enforce the extra freedom, but want to be compatible with GPL, your choices are to either use LGPL or GPL, but know that other people are free to release modifications of your code without respecting your licensing choices.

A danger with dual licensing is that the GPL version can be forked and you lose control of the project, and the ability to sell license free versions (since now the leading version contains code copylefted by people outside of your company)

I've not looked at LGPL, but what you're describing sounds pretty much like you want to be using MPL or CDDL.