I'm in the industry, so I have a little more background on this. They spent about 40M GBP building the system, and it's only been used for two years. It was (entirely?) outsourced to Accenture. Other reasons why the system sucks: It can only handle about 10,000 orders/second, and has latency numbers that are incredibly high (5 milliseconds+).
Looking at other exchanges, there are trading platforms that have been able to last 10+ years while scaling quite well.
TradElect was/is a project management and technical disaster.
Someone on TECHWR-L posted a link to this paper (under the paradoxical title "The Cupertino Effect"), which is about how Excel's autocorrect feature can corrupt statistical analysis of genetic data if/when Excel "makes the wrong assumption" about an entry based on how it looks:
The first 90% of a project takes 90% of the time, the last 10% takes the other 90% of the time.