It's funny how meetups have taken over universities as the place to be for the best knowledge transfer.
As you say, it is way easier to host things at companies, coworking spaces, coffee shops, and pubs.
Universities are exclusive, but they lose quality by being so. They also lose the title of "the place to be" for learning. They're now in third place behind meetups and topic specific internet communities.
KCL has actually been a lot more accommodating since KCL Tech started to take off post-hackathon. We've got great plans in store for the coming year too. Do drop by and say hi! Looking forward to meeting at our events :)
An unbalanced group is, as you say, a problem. The key is to get a wide gamut; people with ideas and some idea of implementation, flat-out implementation people (devs and designers), business people and investors. A lot of the undergrads I know are green but they often have a lot of energy, ideas and can be fine coders.
There is a certain amount of red tape organising events at Universities (my basis for this is KCL and Imperial) unless they are either explicitly educational and you often have to liase with security so we've had a lot less friction by engaging tech companies to host meetings. You get the industry links by making use of their facilities, you get students, devs and business types and in all honesty companies in Silicon Roundabout are gagging to look cool and host a meetup.
Saying that, I'm about to start post-doc work at KCL (been here since Undergrad) so I'll be kicking around for the next 3 yrs so I'll be signing up.