Autodiscover is an integrated part of Lync 2013 which was first introduced in Lync 2010 CU4. Basically, autodiscover was launched for Lync 2010 mobile client and then continued for all Lync 2013 clients. Lync 2013 Windows store app only connects through autodiscover service and does not rely on SRV & other A records.
Lync 2010 mobile clients had connectivity issues from internal network because most of the organizations use private CA for internal services and mobile client does not rely on that. To mitigate this problem, there were work around such as use public certificate for internal network also but this is not very easy because of different DNS names internally and externally or another way was redirect mobile clients to external DNS so that they can connect using public certificate.
You need to create lyncdisoverinternal.domain.com in internal DNS and lyncdiscover.domain.com in external DNS to get the Lync clients connected mainly Lync mobile clients and Lync 2013 Windows store app.
Once Lync 2013 windows clients try to login. The following process mechanism starts to connect to the Lync Server:
While Lync 2013 windows store app try only lyncdiscoverinternal.domain.com and lyncdiscover.domain.com to log in.
In other ways, we can say Lync 2013 mobile connectivity has been hoodwinked. Lync 2013 mobile clients are hard coded to look for a unique parameter which looks for external services to connect regardless of client network location. Lync 2013 mobile clients use Ucwa parameter for internal and external connectivity while Lync 2010 mobile clients use MCX web service parameter for the same.