If any company doesn't have the maturity model it is not 
meaning that it is not maintaining the quality of the 
product or service. It may have the internal QA process and 
the team will be following the same. And some times the 
company may needs to follow the customer process. So in 
this case it will not have the proper maturity model. Still 
it maintains the quality of product or service through the 
internal process or customer process.
It is always possible to maintain good quality without 
proper maturity model.

maturity levels are levels that are obtained when following 
a standard model like CMM. There are several standard 
models.
Many outsourcing companies like to follow a standard 
maturity model to convice customers that there is process 
followed in rolling out a software.
Most developement companies do not follow a industry 
standard model since they have their own process defined to 
roll out a quality software.
The industry standard models are only guidelines to follow 
a methodology to maintain quality in software.Hence any 
internally developed process may be as good or better than 
following a industry standard model cause it may be 
designed keeping the requirements of that company and its 
customers trends in mind.