Some reasoning: It gets (read:forces) you to use the top bar. For people that always ignored the topbar before; they cannot now. So these users, as well as everyone else who used it only sporadically, are now using it always and thus are more likely to investigate and use other links/apps on the topbar now. These of course include all of the other google services. It's like herding cattle.
this seems to me as the most plausible explanation. I reckon the average user might use one or two more google products: maps and gmail. he probably accesses gmail via gmail.com and maps via maps.google.com and never even cared about the black top bar.
EDIT: interesting change: on my local google.ch, the top left google icon is clickable but no hover (hand) icon appears.
I reckon the average user might use one or two more google products: maps and gmail. he probably accesses gmail via gmail.com and maps via maps.google.com
One has a very... unique experience as to who an average user is if one believes the average user understands subdomains. (Or, increasingly, anything that goes into a URL box other than a search term which may occasionally have a .com in it due to legacy branding.)
