While I can understand the disappointment in having a very handy facility withdrawn from a web site, I think you have to stand back and account that old-maps.co.uk is a commercial web site. Regardless of the rights and wrongs of selling such data. I've not used the old maps site for sometime but you can just see information on the current max zoom level.
The problem is of course is that all this current technology becomes a victim of its own success. Those of us who know and use other technologies to enhance or access services can cause problems to those who provide those services. In this case if say you want to use the enhanced zoom feature and then do screen grabs which then can be re-assembled in a graphics package to produce a larger map of what you need then old-maps have lost a sale and you have broken the terms of the End User License.
Another possibility may be that according to the FAQs on the old-maps website, the enhanced zoom facility uses Flash. Now that is a no-no to iPad/iPhone users. OS Openspace are in the process of updating code for both iOS and HTML5. This could be a result of that.
http://maps.cheshire.gov.uk/tithemaps/ The view port is not as big as the old-maps site but if you're just browsing they are adequate and of course its free, not all in one place but free nevertheless.
What's more the Cheshire one has aerials from 1970, Tithe maps etc, very useful site.
Perhaps we should have another thread which just gives links to all Council/County web sites that have the map facility?