I was reading an article about Russian strategy and how they struggle because of their lack of Navy (their main sea ports are easily blockaded) and the article claimed that 'you cannot support major forces from the air alone.'
Are there and examples through history of this being true? The article doesn't cite any precedent for this statement so why would it be true?
Http://www.mauldineconomics.com/this-week-in-geopolitics/mapping-Russia's-strategy
Looking at the Second World War the most obvious example to support the assertion is Stalingrad, where up to 300,000 troops of the German Sixth Army were surrounded from November 1942. The Sixth Army was ordered to dig in rather than try and break out of the pocket, to be supplied by the Luftwaffe. Estimates vary but they would have required around 500-700 tons of supplies per day to hold out, an absolute minimum of 300 tons; at its peak the Luftwaffe was delivering 137 tons per day, averaging closer to 100 tons over the whole siege. It simply wasn't enough, and the remaining Axis troops surrendered in February 1943.
There are counter-examples. Earlier in 1942 smaller German forces were encircled at Kholm and Demyansk and successfully supplied by air until they were relieved. Demyansk, where 100,000 were trapped and kept supplied with an average of 270 - 300 tons per day, could be regarded as a Pyrrhic victory though; the effort cost the Luftwaffe heavily (they lost over 200 aircraft, and had to divert 300 aircraft from aircrew training) and contributed to the belief that air supply was a viable option at Stalingrad.
More successful were Allied efforts in Burma. In February 1944 the headquarters of 7th Indian Division was cut off by a Japanese attack but established a defensive position and, supplied from the air, held out in the Battle of the Admin Box until relieved. On a larger scale garrisons at Kohima and Imphal (around 150,000 troops) were supplied and reinforced by air from March 1944, an average of 275 tons per day delivered, enabling them to halt a Japanese offensive then launch counter-attacks. You could also look at long term air supply efforts over "The Hump" to China from 1942 to 1945 and the Berlin airlift of 1948-49, though these were not to forces in immediate combat.
Air supply is never a long-term option, though, liable to disruption by weather (e.g. monsoons in Burma, snowstorms in Russia) and enemy activity (Allied air superiority was critical over Burma, whereas Luftwaffe transports suffered heavy losses on both the Eastern front and over North Africa, where they were simultaneously operating). As Field Marshal Slim put it in Defeat into Victory:
"Among the most strategically dangerous ideas that half-baked thinking on air supply provoked, was that even if surrounded, positions could be held for months provided that they might be maintained from the air. In fact, troops thus cut off, even if fed and maintained, eventually lost heart and air supply is so easily interrupted; the weather or a few well sited anti-aircraft weapons can easily put a stop to it. Air supply is only half the answer. The other half is an adequate relieving force which, however good the prospect of air supply, must appear in a reasonable time and which the beleaguered garrison must know will appear."
Some further reading: