Advantages to using modified broad: More targeted. Each modified term must be included. This prevents unwanted impressions for partial broad term matches. Misspellings and plurals Order doesn't matter. This is the only keyword targeting option where you can include a list of essential keywords but they don't have to be in a particular order.
I guess there's two answers: 1) 'simple' broad was the original method so it's simply still there as an option, which may well not be the best option for most cases. However as 2) I'd suggest there may still be some cases where a simple broad match is still useful - for example where a single keyword is so specific to a product or service that there's no possibility of confusion/unwanted impressions. However, I do agree that in general if you're going to use broad matches then modified broads are usually better.
Currently you should only use broad match if you really want to let google run wild with where they show your ads. If you bid on Verizon, you will like show on "cell phone." See what I mean. Using modified broad match is kind of like expanding on phrase match, meaning you keyword must be in the search phrase. Only use broad match if you have a well developed negative keyword list.
@ReachMarketingOnline.com I agree. Modified Broad was probably the biggest gift from Google to advertisers. Now we don't have to worry about coming up for non-relevant words and we can expand our reach for our phrase match keywords to account for alternative spellings, order, and forms of the word.
Using broad match without the modifiers is a good way to get a large list of potential keyword ideas. If you have a good grasp of the keywords that convert and the negatives that you want to have in there, then I'm not sure there is much of a benefit to using broad over modified broad. I guess unless you are really just going for volume over conversion.