TL;DR; The VS2010 ISO is small because it excludes MSDN documentation, which is not yet available offline; users can access documentation online instead.

The reason is simple, it has no MSDN documentation in it. I for one never install the MSDN documentation and just use the online version and have always found it a pain to have it inside the same installation, but may people find it useful.
And, why is there no Offline MSDN documentation? The answer is simple, it is not ready yet…
Technorati Tags: ALM
If you've made it this far, it's worth connecting with our principal consultant and coach, Martin Hinshelwood, for a 30-minute 'ask me anything' call.
We partner with businesses across diverse industries, including finance, insurance, healthcare, pharmaceuticals, technology, engineering, transportation, hospitality, entertainment, legal, government, and military sectors.

Xceptor - Process and Data Automation

Illumina

Philips

Schlumberger
NIT A/S

Slaughter and May

Lockheed Martin

SuperControl

Flowmaster (a Mentor Graphics Company)

Brandes Investment Partners L.P.

Workday

Milliman

Lean SA

Slicedbread

ALS Life Sciences
CR2

YearUp.org

Bistech

Nottingham County Council

Washington Department of Enterprise Services

Royal Air Force

New Hampshire Supreme Court

Department of Work and Pensions (UK)

Ghana Police Service

Sage

Illumina

Boeing
CR2

MacDonald Humfrey (Automation) Ltd.

Higher Education Statistics Agency