Now url manager work with regular expressions:
array(
'articles'=>'article/list',
'article/<id:\d+>/*'=>'article/read',
)
But, … php is variant. We do not care about type of var. We just need to know var name.
array(
'articles'=>'article/list',
'article/<id>/*'=>'article/read',
)
Regular expression has a big use in the url manager when you need to build complex urls, an example when creating SEO urls. Your url might be mysite.com/my-pretty-title-234
you may only need the 234 as that is the id (imagine this is a crud controller). Regex is a valuable tool here for parsing such things.
I agree with Jaggi.
If sensorario’s proposition is to be implemented, it could be in the form of a default regex (something like this: “.+?(?=/|$)”) for rules without one.
Moreover, regexps are not the fastest thing on earth.
not the slowest either
I completely agree that regex definitions in the url rules should be kept. They have a fundamental role in the rules.
But Yii is a "high performance framework" not a "not so slow framework"…
With opinions like that, it could easily turn into a “no features framework” as well 
With opinions like that, it’s a “no slow features framework”