You don't need the .disco file from the tutorial. That is only if you want auto-discovery. You do however need the WSDL file, if you intend to be able to involve the web service reference using a dynamic url address.
Unlike most web services that are deployed from a static and well-known endpoint location, SharePoint web services can be invoked from multiple access mappings from multiple virtual paths (/marketing/_vti_bin/search.asmx, /hr/_vti_bin/search.asmx). The custom .WSDL file is meant to provide a dynamic endpoint based on the virtual path you access the web service from.
On SharePoint 2010 you can also easily create a SOAP-based WCF service without having to gernate the disco or wsdl files. Here is my blog post on the subject: