While semantic networks have words in nodes and the arcs are semantic relations, wordnets are definitely more than that: they are:  monolingual dictionaries: they contain words with definitions for each of their senses;  multilingual dictionaries: via the Inter-Lingual Index, ILI, access from one language-specific network to all the others is facilitated; thus, it is possible to compare the organization of the lexical material of various languages, to find examples supporting the thesis of semantic specificity of languages, to introduce the multilingual dimension in various applications relying on wordnets;  thesauri: lexical information is organized in terms of word meanings, not word forms;  lexical ontologies: wordnets contain concepts lexicalizations from various domains and the relations between these concepts lexicalizations.
the high costs involved in terms of money and time prevent other teams to undertake a similar enterprise.