I'm jurist cum developer in Belgium, I spent a decade in this niche:
* Jurists are used to face extraordinary difficulties when researching things. Throw them a monstrous contractor-built Adobe Flex application as a search engine, and they'll be all the happier: still better than hundreds of paper volumes. The erudite knowledge of where and how to search is part of their expertise.
* In their mind, it's the content that matters. The form may be prettier and easier to use, they will hardly notice. As a law student, we had to read and print things presented like this (and this is a extremely gentle example): http://goo.gl/6Uz48Q Years later, I built my own app, where the same content is presented like this (see print preview to see what a little interest in the subject can produce) : http://www.etaamb.be/fr/2015201838.html It doesn't get noticed a lot, although it attracts a lot of visits.
* The sector is cornered with not too innovative academics and conservative publisher companies with vested interests, even more conservative public institutions and associations (lawyers, notaries,... ) and extremely conservative laws. Kickstarting something like an internet app for last wills and testaments without the support of most of them is impossible (been there, done that): there is no place for disruption without institutional support.
* Speaking of institutional support: I only managed to implement an electronic proceedings platform in Belgium (still the only one) because I happen to work at a federal institution. It's been instituted by way of Royal Decree: not really the same as the apple store. It was a fortuitous meeting of ambition and competence: in other settings contractors have to be engaged, of which only the cheapest get selected, resulting in utter crap and millions of wasted taxpayer's money.
* It's very country-specific. Laws and customs stop at national borders, not even speaking of fragmented federal states and small legal districts. You could write a successful app in your country, but other countries have their own hurdles, not event speaking of the not-invented-here bias (As far as I know, technological exchanges are virtually non-existent, even between countries who share a common judicial structure).
Plenty of other stuff in my mind, but still, the sector is ripe for improvement; the internet revolution has just started reaching the outskirts of the legal world. The ways laws are voted, how proceedings and courts work, how doctrinal knowledge is made available and legal professionals joinable, there's plenty of low-hanging fruit. Fruit regulated by state law and pretty tenacious customs ;)